graph/path: implement sophisticated algorithm

Both algorithms are included since the LTA appears to beat the SLTA for
all normal uses, but the SLTA beats the LTA for very large dense graphs.

Leave tools in the benchmark code to allow users to determine which one
they want to use for their data.

graph/path/control_flow_test.go

@@ -138,20 +138,31 @@ func TestDominators(t *testing.T) {
 			g.SetEdge(e)
 		}
 
-		got := Dominators(test.n, g)
-		if !reflect.DeepEqual(got.root, test.want.root) {
-			t.Errorf("unexpected dominator tree root: got:%v want:%v", got.root, test.want.root)
-		}
+		for _, alg := range []struct {
+			name string
+			fn   func(graph.Node, graph.Directed) DominatorTree
+		}{
+			{"Dominators", Dominators},
+			{"DominatorsSLT", DominatorsSLT},
+		} {
+			got := alg.fn(test.n, g)
+			if !reflect.DeepEqual(got.root, test.want.root) {
+				t.Errorf("unexpected dominator tree root from %s: got:%v want:%v",
+					alg.name, got.root, test.want.root)
+			}
 
-		if !reflect.DeepEqual(got.dominatorOf, test.want.dominatorOf) {
-			t.Errorf("unexpected dominator tree: got:%v want:%v", got.dominatorOf, test.want.dominatorOf)
-		}
+			if !reflect.DeepEqual(got.dominatorOf, test.want.dominatorOf) {
+				t.Errorf("unexpected dominator tree from %s: got:%v want:%v",
+					alg.name, got.dominatorOf, test.want.dominatorOf)
+			}
 
-		for _, nodes := range got.dominatedBy {
-			sort.Sort(ordered.ByID(nodes))
-		}
-		if !reflect.DeepEqual(got.dominatedBy, test.want.dominatedBy) {
-			t.Errorf("unexpected dominator tree: got:%v want:%v", got.dominatedBy, test.want.dominatedBy)
+			for _, nodes := range got.dominatedBy {
+				sort.Sort(ordered.ByID(nodes))
+			}
+			if !reflect.DeepEqual(got.dominatedBy, test.want.dominatedBy) {
+				t.Errorf("unexpected dominator tree from %s: got:%v want:%v",
+					alg.name, got.dominatedBy, test.want.dominatedBy)
+			}
 		}
 	}
 }