--- a/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/replacements/WriteBarrierSnippets.java	Thu May 31 10:14:41 2018 -0700
+++ b/src/jdk.internal.vm.compiler/share/classes/org.graalvm.compiler.hotspot/src/org/graalvm/compiler/hotspot/replacements/WriteBarrierSnippets.java	Thu May 31 10:38:05 2018 -0700
@@ -51,6 +51,7 @@
 import org.graalvm.compiler.debug.DebugHandlersFactory;
 import org.graalvm.compiler.graph.Node.ConstantNodeParameter;
 import org.graalvm.compiler.graph.Node.NodeIntrinsic;
+import org.graalvm.compiler.hotspot.GraalHotSpotVMConfig;
 import org.graalvm.compiler.hotspot.meta.HotSpotProviders;
 import org.graalvm.compiler.hotspot.meta.HotSpotRegistersProvider;
 import org.graalvm.compiler.hotspot.nodes.G1ArrayRangePostWriteBarrier;
@@ -65,6 +66,7 @@
 import org.graalvm.compiler.hotspot.nodes.VMErrorNode;
 import org.graalvm.compiler.nodes.NamedLocationIdentity;
 import org.graalvm.compiler.nodes.NodeView;
+import org.graalvm.compiler.nodes.PiNode;
 import org.graalvm.compiler.nodes.StructuredGraph;
 import org.graalvm.compiler.nodes.ValueNode;
 import org.graalvm.compiler.nodes.extended.FixedValueAnchorNode;
@@ -79,12 +81,14 @@
 import org.graalvm.compiler.nodes.type.NarrowOopStamp;
 import org.graalvm.compiler.options.OptionValues;
 import org.graalvm.compiler.replacements.Log;
+import org.graalvm.compiler.replacements.ReplacementsUtil;
 import org.graalvm.compiler.replacements.SnippetCounter;
 import org.graalvm.compiler.replacements.SnippetCounter.Group;
 import org.graalvm.compiler.replacements.SnippetTemplate.AbstractTemplates;
 import org.graalvm.compiler.replacements.SnippetTemplate.Arguments;
 import org.graalvm.compiler.replacements.SnippetTemplate.SnippetInfo;
 import org.graalvm.compiler.replacements.Snippets;
+import org.graalvm.compiler.replacements.nodes.AssertionNode;
 import org.graalvm.compiler.replacements.nodes.DirectStoreNode;
 import org.graalvm.compiler.word.Word;
 import jdk.internal.vm.compiler.word.LocationIdentity;
@@ -140,7 +144,10 @@
     }
 
     @Snippet
-    public static void serialImpreciseWriteBarrier(Object object, @ConstantParameter Counters counters) {
+    public static void serialImpreciseWriteBarrier(Object object, @ConstantParameter boolean verifyBarrier, @ConstantParameter Counters counters) {
+        if (verifyBarrier) {
+            verifyNotArray(object);
+        }
         serialWriteBarrier(Word.objectToTrackedPointer(object), counters);
     }
 
@@ -221,8 +228,8 @@
     }
 
     @Snippet
-    public static void g1PostWriteBarrier(Address address, Object object, Object value, @ConstantParameter boolean usePrecise, @ConstantParameter Register threadRegister,
-                    @ConstantParameter boolean trace, @ConstantParameter Counters counters) {
+    public static void g1PostWriteBarrier(Address address, Object object, Object value, @ConstantParameter boolean usePrecise, @ConstantParameter boolean verifyBarrier,
+                    @ConstantParameter Register threadRegister, @ConstantParameter boolean trace, @ConstantParameter Counters counters) {
         Word thread = registerAsWord(threadRegister);
         Object fixedValue = FixedValueAnchorNode.getObject(value);
         verifyOop(object);
@@ -232,6 +239,9 @@
         if (usePrecise) {
             oop = Word.fromAddress(address);
         } else {
+            if (verifyBarrier) {
+                verifyNotArray(object);
+            }
             oop = Word.objectToTrackedPointer(object);
         }
         int gcCycle = 0;
@@ -298,6 +308,13 @@
         }
     }
 
+    private static void verifyNotArray(Object object) {
+        if (object != null) {
+            // Manually build the null check and cast because we're in snippet that's lowered late.
+            AssertionNode.assertion(false, !PiNode.piCastNonNull(object, Object.class).getClass().isArray(), "imprecise card mark used with array");
+        }
+    }
+
     @Snippet
     public static void g1ArrayRangePreWriteBarrier(Address address, int length, @ConstantParameter int elementStride, @ConstantParameter Register threadRegister) {
         Word thread = registerAsWord(threadRegister);
@@ -415,11 +432,13 @@
 
         private final CompressEncoding oopEncoding;
         private final Counters counters;
+        private final boolean verifyBarrier;
 
-        public Templates(OptionValues options, Iterable<DebugHandlersFactory> factories, SnippetCounter.Group.Factory factory, HotSpotProviders providers, TargetDescription target,
-                        CompressEncoding oopEncoding) {
+        public Templates(OptionValues options, Iterable<DebugHandlersFactory> factories, Group.Factory factory, HotSpotProviders providers, TargetDescription target,
+                        GraalHotSpotVMConfig config) {
             super(options, factories, providers, providers.getSnippetReflection(), target);
-            this.oopEncoding = oopEncoding;
+            this.oopEncoding = config.useCompressedOops ? config.getOopEncoding() : null;
+            this.verifyBarrier = ReplacementsUtil.REPLACEMENTS_ASSERTIONS_ENABLED || config.verifyBeforeGC || config.verifyAfterGC;
             this.counters = new Counters(factory);
         }
 
@@ -432,6 +451,7 @@
                 args = new Arguments(serialImpreciseWriteBarrier, writeBarrier.graph().getGuardsStage(), tool.getLoweringStage());
                 OffsetAddressNode address = (OffsetAddressNode) writeBarrier.getAddress();
                 args.add("object", address.getBase());
+                args.addConst("verifyBarrier", verifyBarrier);
             }
             args.addConst("counters", counters);
             template(writeBarrier, args).instantiate(providers.getMetaAccess(), writeBarrier, DEFAULT_REPLACER, args);
@@ -519,6 +539,7 @@
             args.add("value", value);
 
             args.addConst("usePrecise", writeBarrierPost.usePrecise());
+            args.addConst("verifyBarrier", verifyBarrier);
             args.addConst("threadRegister", registers.getThreadRegister());
             args.addConst("trace", traceBarrier(writeBarrierPost.graph()));
             args.addConst("counters", counters);