pass: some basic allocator test cases

pass/alloc.go

@@ -64,11 +64,15 @@ func (a *Allocator) Add(r reg.Register) {
 }
 
 func (a *Allocator) Allocate() (reg.Allocation, error) {
-	for a.remaining() > 0 {
+	for {
 		if err := a.update(); err != nil {
 			return nil, err
 		}
 
+		if a.remaining() == 0 {
+			break
+		}
+
 		v := a.mostrestricted()
 		if err := a.alloc(v); err != nil {
 			return nil, err

pass/alloc_test.go

@@ -0,0 +1,46 @@
+package pass
+
+import (
+	"testing"
+
+	"github.com/mmcloughlin/avo/reg"
+)
+
+func TestAllocatorSimple(t *testing.T) {
+	c := reg.NewCollection()
+	x, y := c.Xv(), c.Yv()
+
+	a, err := NewAllocatorForKind(reg.SSEAVX)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	a.Add(x)
+	a.Add(y)
+	a.AddInterference(x, y)
+
+	alloc, err := a.Allocate()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	t.Log(alloc)
+
+	if alloc[x] != reg.X0 || alloc[y] != reg.Y1 {
+		t.Fatalf("unexpected allocation")
+	}
+}
+
+func TestAllocatorImpossible(t *testing.T) {
+	a, err := NewAllocatorForKind(reg.SSEAVX)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	a.AddInterference(reg.X7, reg.Z7)
+
+	_, err = a.Allocate()
+	if err == nil {
+		t.Fatal("expected allocation error")
+	}
+}