diff --git a/teavm-core/src/main/java/org/teavm/common/GraphUtils.java b/teavm-core/src/main/java/org/teavm/common/GraphUtils.java
index d181d8e98..ec8fcf277 100644
--- a/teavm-core/src/main/java/org/teavm/common/GraphUtils.java
+++ b/teavm-core/src/main/java/org/teavm/common/GraphUtils.java
@@ -31,37 +31,8 @@ public final class GraphUtils {
     private GraphUtils() {
     }
 
-    public static Graph invert(Graph graph) {
+    public static int[] findBackEdges(Graph graph) {
         int sz = graph.size();
-        GraphBuilder result = new GraphBuilder();
-        int[] sourceEdges = new int[sz];
-        for (int node = 0; node < sz; ++node) {
-            int sourceCount = graph.copyIncomingEdges(node, sourceEdges);
-            for (int i = 0; i < sourceCount; ++i) {
-                int source = sourceEdges[i];
-                result.addEdge(node, source);
-            }
-        }
-        return result.build();
-    }
-
-    public static Graph close(Graph graph) {
-        GraphBuilder result = new GraphBuilder();
-        for (int node = 0; node < graph.size(); ++node) {
-            int[] next = graph.outgoingEdges(node);
-            for (int target : next) {
-                result.addEdge(node, target);
-            }
-            if (next.length == 0) {
-                result.addEdge(node, graph.size());
-            }
-        }
-        return result.build();
-    }
-
-    public static Graph removeLoops(Graph graph) {
-        int sz = graph.size();
-        GraphBuilder result = new GraphBuilder();
         int[] stack = new int[sz * 2];
         int stackSize = 0;
         byte[] state = new byte[sz];
@@ -70,6 +41,7 @@ public final class GraphUtils {
                 stack[stackSize++] = i;
             }
         }
+        IntegerArray result = new IntegerArray(2);
         while (stackSize > 0) {
             int node = stack[--stackSize];
             switch (state[node]) {
@@ -79,11 +51,11 @@ public final class GraphUtils {
                     for (int next : graph.outgoingEdges(node)) {
                         switch (state[next]) {
                             case NONE:
-                                result.addEdge(node, next);
                                 stack[stackSize++] = next;
                                 break;
-                            case VISITED:
-                                result.addEdge(node, next);
+                            case VISITING:
+                                result.add(node);
+                                result.add(next);
                                 break;
                         }
                     }
@@ -93,22 +65,25 @@ public final class GraphUtils {
                     break;
             }
         }
-        return result.build();
+        return result.getAll();
     }
 
-    public static int edgeCount(Graph graph) {
-        int cnt = 0;
-        int sz = graph.size();
-        for (int node = 0; node < sz; ++node) {
-            cnt += graph.outgoingEdgesCount(node);
+    public static boolean isIrreducible(Graph graph) {
+        DominatorTree dom = buildDominatorTree(graph);
+        int[] backEdges = findBackEdges(graph);
+        for (int i = 0; i < backEdges.length; i += 2) {
+            if (!dom.dominates(backEdges[i + 1], backEdges[i])) {
+                return true;
+            }
         }
-        return cnt;
+        return false;
     }
 
     /*
      * Tarjan's algorithm
      */
     public static int[][] findStronglyConnectedComponents(Graph graph, int[] start, GraphNodeFilter filter) {
+        // TODO: can show incorrect behaviour sometimes
         List<int[]> components = new ArrayList<>();
         int[] visitIndex = new int[graph.size()];
         int[] headerIndex = new int[graph.size()];
diff --git a/teavm-core/src/test/java/org/teavm/common/GraphTest.java b/teavm-core/src/test/java/org/teavm/common/GraphTest.java
index bfb8911c6..4ae932305 100644
--- a/teavm-core/src/test/java/org/teavm/common/GraphTest.java
+++ b/teavm-core/src/test/java/org/teavm/common/GraphTest.java
@@ -17,6 +17,8 @@ package org.teavm.common;
 
 import static org.hamcrest.CoreMatchers.*;
 import static org.junit.Assert.*;
+import com.carrotsearch.hppc.IntOpenHashSet;
+import com.carrotsearch.hppc.IntSet;
 import java.util.Arrays;
 import java.util.Comparator;
 import org.junit.Test;
@@ -86,6 +88,71 @@ public class GraphTest {
         assertThat(sccs[0], is(new int[] { 1, 2, 3, 4, 5 }));
     }
 
+    @Test
+    public void irreducibleGraphSplit() {
+        GraphBuilder builder = new GraphBuilder();
+        builder.addEdge(0, 1);
+        builder.addEdge(0, 2);
+        builder.addEdge(0, 3);
+        builder.addEdge(1, 2);
+        builder.addEdge(2, 1);
+        builder.addEdge(3, 2);
+        builder.addEdge(2, 4);
+        builder.addEdge(4, 5);
+        builder.addEdge(4, 1);
+        builder.addEdge(5, 3);
+
+        Graph graph = builder.build();
+        DefaultGraphSplittingBackend backend = new DefaultGraphSplittingBackend(graph);
+        int[] weights = { 1, 4, 1, 10, 1, 1 };
+        GraphUtils.splitIrreducibleGraph(graph, weights, backend);
+        Graph result = backend.getGraph();
+
+        assertTrue("Should be irreducible", GraphUtils.isIrreducible(graph));
+        assertFalse("Should be reducible", GraphUtils.isIrreducible(result));
+        assertTrue("Should be equialent", isEquialent(backend, graph));
+    }
+
+    @Test
+    public void irreducibleGraphSplit2() {
+        GraphBuilder builder = new GraphBuilder();
+        builder.addEdge(0, 1);
+        builder.addEdge(0, 2);
+        builder.addEdge(1, 2);
+        builder.addEdge(2, 1);
+        Graph graph = builder.build();
+
+        DefaultGraphSplittingBackend backend = new DefaultGraphSplittingBackend(graph);
+        int[] weights = new int[graph.size()];
+        Arrays.fill(weights, 1);
+        GraphUtils.splitIrreducibleGraph(graph, weights, backend);
+        Graph result = backend.getGraph();
+
+        assertTrue("Should be irreducible", GraphUtils.isIrreducible(graph));
+        assertFalse("Should be reducible", GraphUtils.isIrreducible(result));
+        assertTrue("Should be equialent", isEquialent(backend, graph));
+    }
+
+    private boolean isEquialent(DefaultGraphSplittingBackend backend, Graph proto) {
+        Graph graph = backend.getGraph();
+        for (int node = 0; node < graph.size(); ++node) {
+            int nodeProto = backend.prototype(node);
+            IntSet succProto = new IntOpenHashSet();
+            for (int succ : graph.outgoingEdges(node)) {
+                succProto.add(backend.prototype(succ));
+            }
+            if (succProto.size() != proto.outgoingEdgesCount(nodeProto)) {
+                return false;
+            }
+            for (int succ : proto.outgoingEdges(nodeProto)) {
+                if (!succProto.contains(succ)) {
+                    return false;
+                }
+            }
+        }
+        return true;
+    }
+
     private GraphNodeFilter filter = new GraphNodeFilter() {
         @Override public boolean match(int node) {
             return true;