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/*
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* Copyright (c) 2013, 2018, Oracle and/or its affiliates. All rights reserved.
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* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
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*
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* This code is free software; you can redistribute it and/or modify it
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* under the terms of the GNU General Public License version 2 only, as
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* published by the Free Software Foundation.
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*
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* This code is distributed in the hope that it will be useful, but WITHOUT
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* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
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* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
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* version 2 for more details (a copy is included in the LICENSE file that
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* accompanied this code).
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*
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* You should have received a copy of the GNU General Public License version
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* 2 along with this work; if not, write to the Free Software Foundation,
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* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
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*
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* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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* or visit www.oracle.com if you need additional information or have any
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* questions.
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*/
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package org.graalvm.compiler.hotspot.phases;
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import java.util.Iterator;
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import org.graalvm.compiler.debug.GraalError;
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import org.graalvm.compiler.graph.Node;
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import org.graalvm.compiler.graph.NodeFlood;
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import org.graalvm.compiler.hotspot.GraalHotSpotVMConfig;
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import org.graalvm.compiler.hotspot.nodes.ArrayRangeWriteBarrier;
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import org.graalvm.compiler.hotspot.nodes.G1PostWriteBarrier;
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import org.graalvm.compiler.hotspot.nodes.ObjectWriteBarrier;
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import org.graalvm.compiler.hotspot.nodes.SerialWriteBarrier;
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import org.graalvm.compiler.nodeinfo.Verbosity;
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import org.graalvm.compiler.nodes.DeoptimizingNode;
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import org.graalvm.compiler.nodes.FixedWithNextNode;
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import org.graalvm.compiler.nodes.LoopBeginNode;
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import org.graalvm.compiler.nodes.StructuredGraph;
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import org.graalvm.compiler.nodes.ValueNode;
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import org.graalvm.compiler.nodes.extended.ArrayRangeWrite;
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import org.graalvm.compiler.nodes.java.LoweredAtomicReadAndWriteNode;
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import org.graalvm.compiler.nodes.java.LogicCompareAndSwapNode;
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import org.graalvm.compiler.nodes.memory.FixedAccessNode;
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import org.graalvm.compiler.nodes.memory.HeapAccess;
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import org.graalvm.compiler.nodes.memory.HeapAccess.BarrierType;
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import org.graalvm.compiler.nodes.memory.ReadNode;
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import org.graalvm.compiler.nodes.memory.WriteNode;
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import org.graalvm.compiler.nodes.memory.address.OffsetAddressNode;
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import org.graalvm.compiler.nodes.type.StampTool;
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import org.graalvm.compiler.nodes.util.GraphUtil;
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import org.graalvm.compiler.phases.Phase;
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/**
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* Verification phase that checks if, for every write, at least one write barrier is present at all
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* paths leading to the previous safepoint. For every write, necessitating a write barrier, a
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* bottom-up traversal of the graph is performed up to the previous safepoints via all possible
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* paths. If, for a certain path, no write barrier satisfying the processed write is found, an
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* assertion is generated.
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*/
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public class WriteBarrierVerificationPhase extends Phase {
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private final GraalHotSpotVMConfig config;
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public WriteBarrierVerificationPhase(GraalHotSpotVMConfig config) {
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this.config = config;
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}
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@Override
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protected void run(StructuredGraph graph) {
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processWrites(graph);
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}
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private void processWrites(StructuredGraph graph) {
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for (Node node : graph.getNodes()) {
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if (isObjectWrite(node) || isObjectArrayRangeWrite(node)) {
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if (node instanceof WriteNode) {
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WriteNode writeNode = (WriteNode) node;
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if (StampTool.isPointerAlwaysNull(writeNode.value())) {
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continue;
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}
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}
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validateWrite(node);
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}
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}
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}
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private void validateWrite(Node write) {
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/*
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* The currently validated write is checked in order to discover if it has an appropriate
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* attached write barrier.
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*/
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if (hasAttachedBarrier((FixedWithNextNode) write)) {
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return;
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}
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NodeFlood frontier = write.graph().createNodeFlood();
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expandFrontier(frontier, write);
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Iterator<Node> iterator = frontier.iterator();
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while (iterator.hasNext()) {
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Node currentNode = iterator.next();
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if (isSafepoint(currentNode)) {
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throw new AssertionError("Write barrier must be present " + write.toString(Verbosity.All) + " / " + write.inputs());
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}
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if (useG1GC()) {
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if (!(currentNode instanceof G1PostWriteBarrier) || (!validateBarrier((FixedAccessNode) write, (ObjectWriteBarrier) currentNode))) {
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expandFrontier(frontier, currentNode);
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}
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} else {
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if (!(currentNode instanceof SerialWriteBarrier) || (!validateBarrier((FixedAccessNode) write, (ObjectWriteBarrier) currentNode)) ||
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((currentNode instanceof SerialWriteBarrier) && !validateBarrier((FixedAccessNode) write, (ObjectWriteBarrier) currentNode))) {
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expandFrontier(frontier, currentNode);
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}
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}
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}
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}
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private boolean useG1GC() {
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return config.useG1GC;
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}
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private boolean hasAttachedBarrier(FixedWithNextNode node) {
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final Node next = node.next();
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final Node previous = node.predecessor();
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boolean validatePreBarrier = useG1GC() && (isObjectWrite(node) || !((ArrayRangeWrite) node).isInitialization());
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if (node instanceof WriteNode) {
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WriteNode writeNode = (WriteNode) node;
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if (writeNode.getLocationIdentity().isInit()) {
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validatePreBarrier = false;
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}
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}
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if (isObjectWrite(node)) {
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return (isObjectBarrier(node, next) || StampTool.isPointerAlwaysNull(getValueWritten(node))) && (!validatePreBarrier || isObjectBarrier(node, previous));
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} else if (isObjectArrayRangeWrite(node)) {
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return (isArrayBarrier(node, next) || StampTool.isPointerAlwaysNull(getValueWritten(node))) && (!validatePreBarrier || isArrayBarrier(node, previous));
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} else {
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return true;
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}
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}
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private static boolean isObjectBarrier(FixedWithNextNode node, final Node next) {
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return next instanceof ObjectWriteBarrier && validateBarrier((FixedAccessNode) node, (ObjectWriteBarrier) next);
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}
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private static boolean isArrayBarrier(FixedWithNextNode node, final Node next) {
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return (next instanceof ArrayRangeWriteBarrier) && ((ArrayRangeWrite) node).getAddress() == ((ArrayRangeWriteBarrier) next).getAddress();
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}
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private static boolean isObjectWrite(Node node) {
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// Read nodes with barrier attached (G1 Ref field) are not validated yet.
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return node instanceof FixedAccessNode && ((HeapAccess) node).getBarrierType() != BarrierType.NONE && !(node instanceof ReadNode);
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}
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private static boolean isObjectArrayRangeWrite(Node node) {
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return node instanceof ArrayRangeWrite && ((ArrayRangeWrite) node).writesObjectArray();
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}
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private static void expandFrontier(NodeFlood frontier, Node node) {
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for (Node previousNode : node.cfgPredecessors()) {
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if (previousNode != null) {
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frontier.add(previousNode);
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}
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}
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}
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private static boolean isSafepoint(Node node) {
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if (node instanceof FixedAccessNode) {
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// Implicit null checks on reads or writes do not count.
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return false;
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}
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/*
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* LoopBegin nodes are also treated as safepoints since a bottom-up analysis is performed
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* and loop safepoints are placed before LoopEnd nodes. Possible elimination of write
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* barriers inside loops, derived from writes outside loops, can not be permitted.
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*/
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return ((node instanceof DeoptimizingNode) && ((DeoptimizingNode) node).canDeoptimize()) || (node instanceof LoopBeginNode);
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}
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private static ValueNode getValueWritten(FixedWithNextNode write) {
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if (write instanceof WriteNode) {
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return ((WriteNode) write).value();
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} else if (write instanceof LogicCompareAndSwapNode) {
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return ((LogicCompareAndSwapNode) write).getNewValue();
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} else if (write instanceof LoweredAtomicReadAndWriteNode) {
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return ((LoweredAtomicReadAndWriteNode) write).getNewValue();
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} else {
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throw GraalError.shouldNotReachHere(String.format("unexpected write node %s", write));
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}
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}
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private static boolean validateBarrier(FixedAccessNode write, ObjectWriteBarrier barrier) {
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assert write instanceof WriteNode || write instanceof LogicCompareAndSwapNode || write instanceof LoweredAtomicReadAndWriteNode : "Node must be of type requiring a write barrier " + write;
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if (!barrier.usePrecise()) {
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if (barrier.getAddress() instanceof OffsetAddressNode && write.getAddress() instanceof OffsetAddressNode) {
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return GraphUtil.unproxify(((OffsetAddressNode) barrier.getAddress()).getBase()) == GraphUtil.unproxify(((OffsetAddressNode) write.getAddress()).getBase());
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}
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}
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return barrier.getAddress() == write.getAddress();
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}
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}
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