pass: allow consecutive labels (#123)

Fixes #122

pass/cfg.go

@@ -11,26 +11,22 @@ import (
 // label name to the following instruction.
 func LabelTarget(fn *ir.Function) error {
 	target := map[ir.Label]*ir.Instruction{}
-	var empty ir.Label
-	pending := empty
+	var pending []ir.Label
 	for _, node := range fn.Nodes {
 		switch n := node.(type) {
 		case ir.Label:
-			if pending != empty {
-				return fmt.Errorf("expected instruction following label %q", pending)
-			}
-			pending = n
-			if _, found := target[pending]; found {
-				return fmt.Errorf("duplicate label \"%s\"", pending)
+			if _, found := target[n]; found {
+				return fmt.Errorf("duplicate label \"%s\"", n)
 			}
+			pending = append(pending, n)
 		case *ir.Instruction:
-			if pending != empty {
-				target[pending] = n
-				pending = empty
+			for _, label := range pending {
+				target[label] = n
 			}
+			pending = nil
 		}
 	}
-	if pending != empty {
+	if len(pending) != 0 {
 		return errors.New("function ends with label")
 	}
 	fn.LabelTarget = target

pass/cfg_test.go

@@ -58,16 +58,25 @@ func TestLabelTargetEndsWithLabel(t *testing.T) {
 	}
 }
 
-func TestLabelTargetInstructionFollowLabel(t *testing.T) {
-	f := ir.NewFunction("expectinstafterlabel")
+func TestLabelTargetConsecutiveLabels(t *testing.T) {
+	i := &ir.Instruction{Opcode: "A"}
+
+	f := ir.NewFunction("consecutivelabels")
 	f.AddLabel(ir.Label("lblA"))
 	f.AddLabel(ir.Label("lblB"))
-	f.AddInstruction(&ir.Instruction{Opcode: "A"})
+	f.AddInstruction(i)
 
-	err := LabelTarget(f)
+	expect := map[ir.Label]*ir.Instruction{
+		"lblA": i,
+		"lblB": i,
+	}
 
-	if err == nil || err.Error() != "expected instruction following label \"lblA\"" {
-		t.Fatalf("expected error when label is not followed by instruction; got %v", err)
+	if err := LabelTarget(f); err != nil {
+		t.Fatal(err)
+	}
+
+	if !reflect.DeepEqual(expect, f.LabelTarget) {
+		t.Fatalf("incorrect LabelTarget value\ngot=%#v\nexpext=%#v\n", f.LabelTarget, expect)
 	}
 }