--- /dev/null	2016-05-31 09:42:47.975716356 -0700
+++ new/src/jdk.vm.compiler/share/classes/org.graalvm.compiler.core/src/org/graalvm/compiler/core/phases/GraphChangeMonitoringPhase.java	2016-12-07 13:48:53.051844548 -0800
@@ -0,0 +1,105 @@
+/*
+ * Copyright (c) 2015, 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.phases;
+
+import java.util.Set;
+import java.util.stream.Collectors;
+
+import org.graalvm.compiler.debug.Debug;
+import org.graalvm.compiler.debug.Debug.Scope;
+import org.graalvm.compiler.graph.Graph.NodeEvent;
+import org.graalvm.compiler.graph.Graph.NodeEventScope;
+import org.graalvm.compiler.graph.Node;
+import org.graalvm.compiler.nodes.LogicConstantNode;
+import org.graalvm.compiler.nodes.StructuredGraph;
+import org.graalvm.compiler.phases.BasePhase;
+import org.graalvm.compiler.phases.PhaseSuite;
+import org.graalvm.compiler.phases.common.util.HashSetNodeEventListener;
+import org.graalvm.compiler.phases.tiers.PhaseContext;
+
+/**
+ * A utility phase for detecting when a phase would change the graph and reporting extra information
+ * about the effects. The phase is first run on a copy of the graph and if a change in that graph is
+ * detected then it's rerun on the original graph inside a new debug scope under
+ * GraphChangeMonitoringPhase. The message argument can be used to distinguish between the same
+ * phase run at different points.
+ *
+ * @param <C>
+ */
+public class GraphChangeMonitoringPhase<C extends PhaseContext> extends PhaseSuite<C> {
+
+    private final String message;
+
+    public GraphChangeMonitoringPhase(String message, BasePhase<C> phase) {
+        super();
+        this.message = message;
+        appendPhase(phase);
+    }
+
+    public GraphChangeMonitoringPhase(String message) {
+        super();
+        this.message = message;
+    }
+
+    @Override
+    @SuppressWarnings("try")
+    protected void run(StructuredGraph graph, C context) {
+        /*
+         * Phase may add nodes but not end up using them so ignore additions. Nodes going dead and
+         * having their inputs change are the main interesting differences.
+         */
+        HashSetNodeEventListener listener = new HashSetNodeEventListener().exclude(NodeEvent.NODE_ADDED);
+        StructuredGraph graphCopy = (StructuredGraph) graph.copy();
+        try (NodeEventScope s = graphCopy.trackNodeEvents(listener)) {
+            try (Scope s2 = Debug.sandbox("WithoutMonitoring", null)) {
+                super.run(graphCopy, context);
+            } catch (Throwable t) {
+                Debug.handle(t);
+            }
+        }
+        /*
+         * Ignore LogicConstantNode since those are sometimes created and deleted as part of running
+         * a phase.
+         */
+        if (listener.getNodes().stream().filter(e -> !(e instanceof LogicConstantNode)).findFirst().isPresent()) {
+            /* rerun it on the real graph in a new Debug scope so Dump and Log can find it. */
+            listener = new HashSetNodeEventListener();
+            try (NodeEventScope s = graph.trackNodeEvents(listener)) {
+                try (Scope s2 = Debug.scope("WithGraphChangeMonitoring")) {
+                    if (Debug.isDumpEnabled(Debug.BASIC_LOG_LEVEL)) {
+                        Debug.dump(Debug.BASIC_LOG_LEVEL, graph, "*** Before phase %s", getName());
+                    }
+                    super.run(graph, context);
+                    Set<Node> collect = listener.getNodes().stream().filter(e -> !e.isAlive()).filter(e -> !(e instanceof LogicConstantNode)).collect(Collectors.toSet());
+                    if (Debug.isDumpEnabled(Debug.BASIC_LOG_LEVEL)) {
+                        Debug.dump(Debug.BASIC_LOG_LEVEL, graph, "*** After phase %s %s", getName(), collect);
+                    }
+                    Debug.log("*** %s %s %s\n", message, graph, collect);
+                }
+            }
+        } else {
+            // Go ahead and run it normally even though it should have no effect
+            super.run(graph, context);
+        }
+    }
+}