--- /dev/null	2017-01-22 10:16:57.869617664 -0800
+++ new/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.core.common/src/org/graalvm/compiler/core/common/cfg/CFGVerifier.java	2017-02-15 16:57:04.884630508 -0800
@@ -0,0 +1,125 @@
+/*
+ * Copyright (c) 2012, 2014, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+package org.graalvm.compiler.core.common.cfg;
+
+import java.util.ArrayDeque;
+import java.util.Arrays;
+import java.util.Deque;
+
+public class CFGVerifier {
+
+    public static <T extends AbstractBlockBase<T>, C extends AbstractControlFlowGraph<T>> boolean verify(C cfg) {
+        for (T block : cfg.getBlocks()) {
+            assert block.getId() >= 0;
+            assert cfg.getBlocks()[block.getId()] == block;
+
+            for (T pred : block.getPredecessors()) {
+                assert Arrays.asList(pred.getSuccessors()).contains(block);
+                assert pred.getId() < block.getId() || pred.isLoopEnd();
+            }
+
+            for (T sux : block.getSuccessors()) {
+                assert Arrays.asList(sux.getPredecessors()).contains(block);
+                assert sux.getId() > block.getId() || sux.isLoopHeader();
+            }
+
+            if (block.getDominator() != null) {
+                assert block.getDominator().getId() < block.getId();
+                assert block.getDominator().getDominated().contains(block);
+            }
+            for (T dominated : block.getDominated()) {
+                assert dominated.getId() > block.getId();
+                assert dominated.getDominator() == block;
+            }
+
+            T postDominatorBlock = block.getPostdominator();
+            if (postDominatorBlock != null) {
+                assert block.getSuccessorCount() > 0 : "block has post-dominator block, but no successors";
+
+                BlockMap<Boolean> visitedBlocks = new BlockMap<>(cfg);
+                visitedBlocks.put(block, true);
+
+                Deque<T> stack = new ArrayDeque<>();
+                for (T sux : block.getSuccessors()) {
+                    visitedBlocks.put(sux, true);
+                    stack.push(sux);
+                }
+
+                while (stack.size() > 0) {
+                    T tos = stack.pop();
+                    assert tos.getId() <= postDominatorBlock.getId();
+                    if (tos == postDominatorBlock) {
+                        continue; // found a valid path
+                    }
+                    assert tos.getSuccessorCount() > 0 : "no path found";
+
+                    for (T sux : tos.getSuccessors()) {
+                        if (visitedBlocks.get(sux) == null) {
+                            visitedBlocks.put(sux, true);
+                            stack.push(sux);
+                        }
+                    }
+                }
+            }
+
+            assert cfg.getLoops() == null || !block.isLoopHeader() || block.getLoop().getHeader() == block;
+        }
+
+        if (cfg.getLoops() != null) {
+            for (Loop<T> loop : cfg.getLoops()) {
+                assert loop.getHeader().isLoopHeader();
+
+                for (T block : loop.getBlocks()) {
+                    assert block.getId() >= loop.getHeader().getId();
+
+                    Loop<?> blockLoop = block.getLoop();
+                    while (blockLoop != loop) {
+                        assert blockLoop != null;
+                        blockLoop = blockLoop.getParent();
+                    }
+
+                    if (!(block.isLoopHeader() && block.getLoop() == loop)) {
+                        for (T pred : block.getPredecessors()) {
+                            if (!loop.getBlocks().contains(pred)) {
+                                assert false : "Loop " + loop + " does not contain " + pred;
+                                return false;
+                            }
+                        }
+                    }
+                }
+
+                for (T block : loop.getExits()) {
+                    assert block.getId() >= loop.getHeader().getId();
+
+                    Loop<?> blockLoop = block.getLoop();
+                    while (blockLoop != null) {
+                        blockLoop = blockLoop.getParent();
+                        assert blockLoop != loop;
+                    }
+                }
+            }
+        }
+
+        return true;
+    }
+}