wasm gc: implement System.identityHashCode() and some Integer intrinsics

classlib/src/main/java/org/teavm/classlib/java/lang/TObject.java

@@ -15,6 +15,7 @@
  */
 package org.teavm.classlib.java.lang;
 
+import org.teavm.backend.wasm.runtime.WasmGCSupport;
 import org.teavm.classlib.PlatformDetector;
 import org.teavm.dependency.PluggableDependency;
 import org.teavm.interop.Address;
@@ -246,7 +247,22 @@ public class TObject {
     }
 
     final int identity() {
-        if (PlatformDetector.isLowLevel()) {
+        if (PlatformDetector.isWebAssemblyGC()) {
+            var identity = wasmGCIdentity();
+            if (identity < 0) {
+                var monitor = this.monitor;
+                if (monitor != null) {
+                    if (monitor.id < 0) {
+                        monitor.id = WasmGCSupport.nextObjectId() & 0x7ffffff;
+                    }
+                    return monitor.id;
+                } else {
+                    identity = WasmGCSupport.nextObjectId();
+                    setWasmGCIdentity(identity);
+                }
+            }
+            return identity;
+        } else if (PlatformDetector.isLowLevel()) {
             Monitor monitor = this.monitor;
             if (monitor == null) {
                 int hashCode = hashCodeLowLevel(this);
@@ -271,6 +287,10 @@ public class TObject {
         return Platform.getPlatformObject(this).getId();
     }
 
+    private native int wasmGCIdentity();
+
+    private native void setWasmGCIdentity(int identity);
+
     @DelegateTo("hashCodeLowLevelImpl")
     @NoSideEffects
     @Unmanaged

core/src/main/java/org/teavm/backend/wasm/disasm/DisassemblyCodeSectionListener.java

@@ -135,6 +135,8 @@ public class DisassemblyCodeSectionListener implements AddressListener, CodeSect
                         return "extern";
                     case STRUCT:
                         return "struct";
+                    case I31:
+                        return "i31";
                     default:
                         throw new IllegalArgumentException();
                 }
@@ -829,8 +831,21 @@ public class DisassemblyCodeSectionListener implements AddressListener, CodeSect
     }
 
     @Override
-    public void cast(WasmHollowType.Reference type) {
+    public void cast(WasmHollowType.Reference type, boolean nullable) {
-        writer.address(address).write("ref.cast ").write(typeToString(type)).eol();
+        writer.address(address).write("ref.cast (ref ");
+        if (!nullable) {
+            writer.write("null ");
+        }
+        writer.write(typeToString(type)).write(")").eol();
+    }
+
+    @Override
+    public void test(WasmHollowType.Reference type, boolean nullable) {
+        writer.address(address).write("ref.test (ref ");
+        if (!nullable) {
+            writer.write("null ");
+        }
+        writer.write(typeToString(type)).write(")").eol();
     }
 
     @Override
@@ -890,6 +905,16 @@ public class DisassemblyCodeSectionListener implements AddressListener, CodeSect
         writer.address(address).write("ref.func ").write(Integer.toString(functionIndex)).eol();
     }
 
+    @Override
+    public void int31Reference() {
+        writer.address(address).write("ref.i31").eol();
+    }
+
+    @Override
+    public void int31Get(WasmSignedType signedType) {
+        writer.address(address).write("ref.i31_").write(signedType == WasmSignedType.SIGNED ? "s" : "u").eol();
+    }
+
     public static void main(String[] args) throws IOException {
         var file = new File(args[0]);
         var bytes = Files.readAllBytes(file.toPath());

core/src/main/java/org/teavm/backend/wasm/generate/gc/methods/WasmGCGenerationVisitor.java

@@ -26,6 +26,7 @@ import org.teavm.ast.SubscriptExpr;
 import org.teavm.backend.wasm.BaseWasmFunctionRepository;
 import org.teavm.backend.wasm.WasmFunctionTypes;
 import org.teavm.backend.wasm.gc.PreciseTypeInference;
+import org.teavm.backend.wasm.generate.TemporaryVariablePool;
 import org.teavm.backend.wasm.generate.common.methods.BaseWasmGenerationVisitor;
 import org.teavm.backend.wasm.generate.gc.classes.WasmGCClassInfoProvider;
 import org.teavm.backend.wasm.generate.gc.classes.WasmGCTypeMapper;
@@ -587,5 +588,10 @@ public class WasmGCGenerationVisitor extends BaseWasmGenerationVisitor {
         public WasmGCClassInfoProvider classInfoProvider() {
             return context.classInfoProvider();
         }
+
+        @Override
+        public TemporaryVariablePool tempVars() {
+            return tempVars;
+        }
     };
 }

core/src/main/java/org/teavm/backend/wasm/intrinsics/gc/IntNumIntrinsic.java

@@ -24,23 +24,28 @@ import org.teavm.backend.wasm.model.expression.WasmIntBinaryOperation;
 import org.teavm.backend.wasm.model.expression.WasmIntType;
 import org.teavm.model.MethodReference;
 
-public class LongIntrinsic implements WasmGCIntrinsic {
+public class IntNumIntrinsic implements WasmGCIntrinsic {
-    private static final MethodReference COMPARE_UNSIGNED = new MethodReference(WasmRuntime.class,
+    private final MethodReference compareUnsigned;
-            "compareUnsigned", long.class, long.class, int.class);
+    private final WasmIntType wasmType;
+
+    public IntNumIntrinsic(Class<?> javaType, WasmIntType wasmType) {
+        compareUnsigned = new MethodReference(WasmRuntime.class, "compareUnsigned", javaType, javaType, int.class);
+        this.wasmType = wasmType;
+    }
 
     @Override
     public WasmExpression apply(InvocationExpr invocation, WasmGCIntrinsicContext context) {
         switch (invocation.getMethod().getName()) {
             case "divideUnsigned":
-                return new WasmIntBinary(WasmIntType.INT64, WasmIntBinaryOperation.DIV_UNSIGNED,
+                return new WasmIntBinary(wasmType, WasmIntBinaryOperation.DIV_UNSIGNED,
                         context.generate(invocation.getArguments().get(0)),
                         context.generate(invocation.getArguments().get(1)));
             case "remainderUnsigned":
-                return new WasmIntBinary(WasmIntType.INT64, WasmIntBinaryOperation.REM_UNSIGNED,
+                return new WasmIntBinary(wasmType, WasmIntBinaryOperation.REM_UNSIGNED,
                         context.generate(invocation.getArguments().get(0)),
                         context.generate(invocation.getArguments().get(1)));
             case "compareUnsigned":
-                return new WasmCall(context.functions().forStaticMethod(COMPARE_UNSIGNED),
+                return new WasmCall(context.functions().forStaticMethod(compareUnsigned),
                         context.generate(invocation.getArguments().get(0)),
                         context.generate(invocation.getArguments().get(1)));
             default:

core/src/main/java/org/teavm/backend/wasm/intrinsics/gc/ObjectIntrinsic.java

@@ -0,0 +1,130 @@
+/*
+ *  Copyright 2024 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.backend.wasm.intrinsics.gc;
+
+import org.teavm.ast.InvocationExpr;
+import org.teavm.backend.wasm.generate.gc.classes.WasmGCClassInfoProvider;
+import org.teavm.backend.wasm.model.WasmType;
+import org.teavm.backend.wasm.model.expression.WasmBlock;
+import org.teavm.backend.wasm.model.expression.WasmBranch;
+import org.teavm.backend.wasm.model.expression.WasmCast;
+import org.teavm.backend.wasm.model.expression.WasmDrop;
+import org.teavm.backend.wasm.model.expression.WasmExpression;
+import org.teavm.backend.wasm.model.expression.WasmGetLocal;
+import org.teavm.backend.wasm.model.expression.WasmInt31Get;
+import org.teavm.backend.wasm.model.expression.WasmInt31Reference;
+import org.teavm.backend.wasm.model.expression.WasmInt32Constant;
+import org.teavm.backend.wasm.model.expression.WasmIntType;
+import org.teavm.backend.wasm.model.expression.WasmIntUnary;
+import org.teavm.backend.wasm.model.expression.WasmIntUnaryOperation;
+import org.teavm.backend.wasm.model.expression.WasmNullConstant;
+import org.teavm.backend.wasm.model.expression.WasmSetLocal;
+import org.teavm.backend.wasm.model.expression.WasmSignedType;
+import org.teavm.backend.wasm.model.expression.WasmStructGet;
+import org.teavm.backend.wasm.model.expression.WasmStructSet;
+import org.teavm.backend.wasm.model.expression.WasmTest;
+import org.teavm.model.ValueType;
+
+public class ObjectIntrinsic implements WasmGCIntrinsic {
+    @Override
+    public WasmExpression apply(InvocationExpr invocation, WasmGCIntrinsicContext context) {
+        switch (invocation.getMethod().getName()) {
+            case "getClass":
+                return generateGetClass(invocation, context);
+            case "getMonitor":
+                return generateGetMonitor(invocation, context);
+            case "setMonitor":
+                return generateSetMonitor(invocation, context);
+            case "wasmGCIdentity":
+                return generateGetIdentity(invocation, context);
+            case "setWasmGCIdentity":
+                return generateSetIdentity(invocation, context);
+            default:
+                throw new IllegalArgumentException();
+        }
+    }
+
+    private WasmExpression generateGetClass(InvocationExpr invocation, WasmGCIntrinsicContext context) {
+        var obj = context.generate(invocation.getArguments().get(0));
+        var objectStruct = context.classInfoProvider().getClassInfo("java.lang.Object").getStructure();
+        var result = new WasmStructGet(objectStruct, obj, WasmGCClassInfoProvider.CLASS_FIELD_OFFSET);
+        result.setLocation(invocation.getLocation());
+        return result;
+    }
+
+    private WasmExpression generateGetMonitor(InvocationExpr invocation, WasmGCIntrinsicContext context) {
+        var monitorType = context.classInfoProvider().getClassInfo(ValueType.object("java.lang.Object$Monitor"))
+                .getStructure().getReference();
+        var objectStruct = context.classInfoProvider().getClassInfo(ValueType.object("java.lang.Object"))
+                .getStructure();
+        var block = new WasmBlock(false);
+        block.setType(monitorType);
+        var tmpVar = context.tempVars().acquire(WasmType.Reference.ANY);
+        var instance = context.generate(invocation.getArguments().get(0));
+        block.getBody().add(new WasmSetLocal(tmpVar, new WasmStructGet(objectStruct, instance,
+                WasmGCClassInfoProvider.MONITOR_FIELD_OFFSET)));
+
+        WasmExpression test = new WasmTest(new WasmGetLocal(tmpVar), monitorType, false);
+        test = new WasmIntUnary(WasmIntType.INT32, WasmIntUnaryOperation.EQZ, test);
+        var branch = new WasmBranch(test, block);
+        branch.setResult(new WasmNullConstant(monitorType));
+        block.getBody().add(new WasmDrop(branch));
+
+        block.getBody().add(new WasmCast(new WasmGetLocal(tmpVar), monitorType));
+        context.tempVars().release(tmpVar);
+        return block;
+    }
+
+    private WasmExpression generateSetMonitor(InvocationExpr invocation, WasmGCIntrinsicContext context) {
+        var objectStruct = context.classInfoProvider().getClassInfo(ValueType.object("java.lang.Object"))
+                .getStructure();
+        var instance = context.generate(invocation.getArguments().get(0));
+        var monitor = context.generate(invocation.getArguments().get(1));
+        return new WasmStructSet(objectStruct, instance, WasmGCClassInfoProvider.MONITOR_FIELD_OFFSET, monitor);
+    }
+
+    private WasmExpression generateGetIdentity(InvocationExpr invocation, WasmGCIntrinsicContext context) {
+        var objectStruct = context.classInfoProvider().getClassInfo(ValueType.object("java.lang.Object"))
+                .getStructure();
+        var block = new WasmBlock(false);
+        block.setType(WasmType.INT32);
+        var tmpVar = context.tempVars().acquire(WasmType.Reference.ANY);
+        var instance = context.generate(invocation.getArguments().get(0));
+        block.getBody().add(new WasmSetLocal(tmpVar, new WasmStructGet(objectStruct, instance,
+                WasmGCClassInfoProvider.MONITOR_FIELD_OFFSET)));
+
+        WasmExpression test = new WasmTest(new WasmGetLocal(tmpVar), WasmType.Reference.I31, false);
+        test = new WasmIntUnary(WasmIntType.INT32, WasmIntUnaryOperation.EQZ, test);
+        var branch = new WasmBranch(test, block);
+        branch.setResult(new WasmInt32Constant(-1));
+        block.getBody().add(new WasmDrop(branch));
+
+        var i31ref = new WasmCast(new WasmGetLocal(tmpVar), WasmType.Reference.I31);
+        block.getBody().add(new WasmInt31Get(i31ref, WasmSignedType.UNSIGNED));
+        context.tempVars().release(tmpVar);
+        return block;
+    }
+
+    private WasmExpression generateSetIdentity(InvocationExpr invocation, WasmGCIntrinsicContext context) {
+        var objectStruct = context.classInfoProvider().getClassInfo(ValueType.object("java.lang.Object"))
+                .getStructure();
+        var instance = context.generate(invocation.getArguments().get(0));
+        var identity = context.generate(invocation.getArguments().get(1));
+        var identityWrapper = new WasmInt31Reference(identity);
+        return new WasmStructSet(objectStruct, instance, WasmGCClassInfoProvider.MONITOR_FIELD_OFFSET,
+                identityWrapper);
+    }
+}

core/src/main/java/org/teavm/backend/wasm/intrinsics/gc/ObjectIntrinsics.java

@@ -1,32 +0,0 @@
-/*
- *  Copyright 2024 Alexey Andreev.
- *
- *  Licensed under the Apache License, Version 2.0 (the "License");
- *  you may not use this file except in compliance with the License.
- *  You may obtain a copy of the License at
- *
- *       http://www.apache.org/licenses/LICENSE-2.0
- *
- *  Unless required by applicable law or agreed to in writing, software
- *  distributed under the License is distributed on an "AS IS" BASIS,
- *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- *  See the License for the specific language governing permissions and
- *  limitations under the License.
- */
-package org.teavm.backend.wasm.intrinsics.gc;
-
-import org.teavm.ast.InvocationExpr;
-import org.teavm.backend.wasm.generate.gc.classes.WasmGCClassInfoProvider;
-import org.teavm.backend.wasm.model.expression.WasmExpression;
-import org.teavm.backend.wasm.model.expression.WasmStructGet;
-
-public class ObjectIntrinsics implements WasmGCIntrinsic {
-    @Override
-    public WasmExpression apply(InvocationExpr invocation, WasmGCIntrinsicContext context) {
-        var obj = context.generate(invocation.getArguments().get(0));
-        var objectStruct = context.classInfoProvider().getClassInfo("java.lang.Object").getStructure();
-        var result = new WasmStructGet(objectStruct, obj, WasmGCClassInfoProvider.CLASS_FIELD_OFFSET);
-        result.setLocation(invocation.getLocation());
-        return result;
-    }
-}

core/src/main/java/org/teavm/backend/wasm/intrinsics/gc/WasmGCIntrinsicContext.java

@@ -19,6 +19,7 @@ import org.teavm.ast.Expr;
 import org.teavm.backend.wasm.BaseWasmFunctionRepository;
 import org.teavm.backend.wasm.WasmFunctionTypes;
 import org.teavm.backend.wasm.gc.PreciseTypeInference;
+import org.teavm.backend.wasm.generate.TemporaryVariablePool;
 import org.teavm.backend.wasm.generate.gc.classes.WasmGCClassInfoProvider;
 import org.teavm.backend.wasm.generate.gc.classes.WasmGCTypeMapper;
 import org.teavm.backend.wasm.model.WasmModule;
@@ -41,4 +42,6 @@ public interface WasmGCIntrinsicContext {
     WasmGCTypeMapper typeMapper();
 
     WasmGCClassInfoProvider classInfoProvider();
+
+    TemporaryVariablePool tempVars();
 }

core/src/main/java/org/teavm/backend/wasm/intrinsics/gc/WasmGCIntrinsics.java

@@ -20,7 +20,9 @@ import java.util.List;
 import java.util.Map;
 import org.teavm.backend.wasm.WasmRuntime;
 import org.teavm.backend.wasm.generate.gc.methods.WasmGCIntrinsicProvider;
+import org.teavm.backend.wasm.model.expression.WasmIntType;
 import org.teavm.model.MethodReference;
+import org.teavm.model.ValueType;
 
 public class WasmGCIntrinsics implements WasmGCIntrinsicProvider {
     private Map<MethodReference, WasmGCIntrinsic> intrinsics = new HashMap<>();
@@ -30,7 +32,7 @@ public class WasmGCIntrinsics implements WasmGCIntrinsicProvider {
         fillObject();
         fillClass();
         fillSystem();
-        fillLong();
+        fillLongAndInteger();
     }
 
     private void fillWasmRuntime() {
@@ -50,8 +52,16 @@ public class WasmGCIntrinsics implements WasmGCIntrinsicProvider {
     }
 
     private void fillObject() {
-        var objectIntrinsics = new ObjectIntrinsics();
+        var objectIntrinsics = new ObjectIntrinsic();
         intrinsics.put(new MethodReference(Object.class, "getClass", Class.class), objectIntrinsics);
+        intrinsics.put(new MethodReference(Object.class.getName(), "getMonitor",
+                ValueType.object("java.lang.Object$Monitor")), objectIntrinsics);
+        intrinsics.put(new MethodReference(Object.class.getName(), "setMonitor",
+                ValueType.object("java.lang.Object$Monitor"), ValueType.VOID), objectIntrinsics);
+        intrinsics.put(new MethodReference(Object.class.getName(), "wasmGCIdentity", ValueType.INTEGER),
+                objectIntrinsics);
+        intrinsics.put(new MethodReference(Object.class.getName(), "setWasmGCIdentity", ValueType.INTEGER,
+                ValueType.VOID), objectIntrinsics);
     }
 
     private void fillClass() {
@@ -66,13 +76,18 @@ public class WasmGCIntrinsics implements WasmGCIntrinsicProvider {
                 int.class, int.class, void.class), new SystemArrayCopyIntrinsic());
     }
 
-    private void fillLong() {
+    private void fillLongAndInteger() {
-        var intrinsic = new LongIntrinsic();
+        fillIntNum(int.class, Integer.class, WasmIntType.INT32);
-        intrinsics.put(new MethodReference(Long.class, "divideUnsigned", long.class, long.class, long.class),
+        fillIntNum(long.class, Long.class, WasmIntType.INT64);
+    }
+
+    private void fillIntNum(Class<?> javaClass, Class<?> wrapperClass, WasmIntType wasmType) {
+        var intrinsic = new IntNumIntrinsic(javaClass, wasmType);
+        intrinsics.put(new MethodReference(wrapperClass, "divideUnsigned", javaClass, javaClass, javaClass),
                 intrinsic);
-        intrinsics.put(new MethodReference(Long.class, "remainderUnsigned", long.class, long.class, long.class),
+        intrinsics.put(new MethodReference(wrapperClass, "remainderUnsigned", javaClass, javaClass, javaClass),
                 intrinsic);
-        intrinsics.put(new MethodReference(Long.class, "compareUnsigned", long.class, long.class, int.class),
+        intrinsics.put(new MethodReference(wrapperClass, "compareUnsigned", javaClass, javaClass, int.class),
                 intrinsic);
     }
 

core/src/main/java/org/teavm/backend/wasm/model/WasmType.java

@@ -62,6 +62,7 @@ public abstract class WasmType {
         public static final SpecialReference EXTERN = SpecialReferenceKind.EXTERN.asType();
         public static final SpecialReference STRUCT = SpecialReferenceKind.STRUCT.asType();
         public static final SpecialReference ARRAY = SpecialReferenceKind.ARRAY.asType();
+        public static final SpecialReference I31 = SpecialReferenceKind.I31.asType();
     }
 
     public static final class CompositeReference extends Reference {
@@ -85,7 +86,8 @@ public abstract class WasmType {
         ANY,
         EXTERN,
         STRUCT,
-        ARRAY;
+        ARRAY,
+        I31;
 
         private SpecialReference type;
 

core/src/main/java/org/teavm/backend/wasm/model/expression/WasmCast.java

@@ -21,10 +21,16 @@ import org.teavm.backend.wasm.model.WasmType;
 public class WasmCast extends WasmExpression {
     private WasmExpression value;
     private WasmType.Reference targetType;
+    private boolean nullable;
 
     public WasmCast(WasmExpression value, WasmType.Reference targetType) {
+        this(value, targetType, true);
+    }
+
+    public WasmCast(WasmExpression value, WasmType.Reference targetType, boolean nullable) {
         this.value = Objects.requireNonNull(value);
         this.targetType = Objects.requireNonNull(targetType);
+        this.nullable = nullable;
     }
 
     public WasmExpression getValue() {
@@ -43,6 +49,14 @@ public class WasmCast extends WasmExpression {
         this.targetType = Objects.requireNonNull(targetType);
     }
 
+    public boolean isNullable() {
+        return nullable;
+    }
+
+    public void setNullable(boolean nullable) {
+        this.nullable = nullable;
+    }
+
     @Override
     public void acceptVisitor(WasmExpressionVisitor visitor) {
         visitor.visit(this);

core/src/main/java/org/teavm/backend/wasm/model/expression/WasmDefaultExpressionVisitor.java

@@ -251,6 +251,11 @@ public class WasmDefaultExpressionVisitor implements WasmExpressionVisitor {
         expression.getValue().acceptVisitor(this);
     }
 
+    @Override
+    public void visit(WasmTest expression) {
+        expression.getValue().acceptVisitor(this);
+    }
+
     @Override
     public void visit(WasmStructNew expression) {
         for (var initializer : expression.getInitializers()) {
@@ -308,4 +313,14 @@ public class WasmDefaultExpressionVisitor implements WasmExpressionVisitor {
     @Override
     public void visit(WasmFunctionReference expression) {
     }
+
+    @Override
+    public void visit(WasmInt31Reference expression) {
+        expression.getValue().acceptVisitor(this);
+    }
+
+    @Override
+    public void visit(WasmInt31Get expression) {
+        expression.getValue().acceptVisitor(this);
+    }
 }

core/src/main/java/org/teavm/backend/wasm/model/expression/WasmExpressionVisitor.java

@@ -96,6 +96,8 @@ public interface WasmExpressionVisitor {
 
     void visit(WasmCast expression);
 
+    void visit(WasmTest expression);
+
     void visit(WasmStructNew expression);
 
     void visit(WasmStructNewDefault expression);
@@ -115,4 +117,8 @@ public interface WasmExpressionVisitor {
     void visit(WasmArrayCopy expression);
 
     void visit(WasmFunctionReference expression);
+
+    void visit(WasmInt31Reference expression);
+
+    void visit(WasmInt31Get expression);
 }

core/src/main/java/org/teavm/backend/wasm/model/expression/WasmInt31Get.java

@@ -0,0 +1,49 @@
+/*
+ *  Copyright 2024 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.backend.wasm.model.expression;
+
+import java.util.Objects;
+
+public class WasmInt31Get extends WasmExpression {
+    private WasmSignedType signedType;
+    private WasmExpression value;
+
+    public WasmInt31Get(WasmExpression value, WasmSignedType signedType) {
+        this.signedType = Objects.requireNonNull(signedType);
+        this.value = Objects.requireNonNull(value);
+    }
+
+    public WasmSignedType getSignedType() {
+        return signedType;
+    }
+
+    public void setSignedType(WasmSignedType signedType) {
+        this.signedType = Objects.requireNonNull(signedType);
+    }
+
+    public WasmExpression getValue() {
+        return value;
+    }
+
+    public void setValue(WasmExpression value) {
+        this.value = Objects.requireNonNull(value);
+    }
+
+    @Override
+    public void acceptVisitor(WasmExpressionVisitor visitor) {
+        visitor.visit(this);
+    }
+}

core/src/main/java/org/teavm/backend/wasm/model/expression/WasmInt31Reference.java

@@ -0,0 +1,39 @@
+/*
+ *  Copyright 2024 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.backend.wasm.model.expression;
+
+import java.util.Objects;
+
+public class WasmInt31Reference extends WasmExpression {
+    private WasmExpression value;
+
+    public WasmInt31Reference(WasmExpression value) {
+        this.value = Objects.requireNonNull(value);
+    }
+
+    public WasmExpression getValue() {
+        return value;
+    }
+
+    public void setValue(WasmExpression value) {
+        this.value = Objects.requireNonNull(value);
+    }
+
+    @Override
+    public void acceptVisitor(WasmExpressionVisitor visitor) {
+        visitor.visit(this);
+    }
+}

core/src/main/java/org/teavm/backend/wasm/model/expression/WasmReplacingExpressionVisitor.java

@@ -300,6 +300,12 @@ public class WasmReplacingExpressionVisitor implements WasmExpressionVisitor {
         expression.setValue(mapper.apply(expression.getValue()));
     }
 
+    @Override
+    public void visit(WasmTest expression) {
+        expression.getValue().acceptVisitor(this);
+        expression.setValue(mapper.apply(expression.getValue()));
+    }
+
     @Override
     public void visit(WasmStructNew expression) {
         replaceExpressions(expression.getInitializers());
@@ -378,4 +384,16 @@ public class WasmReplacingExpressionVisitor implements WasmExpressionVisitor {
     @Override
     public void visit(WasmFunctionReference expression) {
     }
+
+    @Override
+    public void visit(WasmInt31Reference expression) {
+        expression.getValue().acceptVisitor(this);
+        expression.setValue(mapper.apply(expression.getValue()));
+    }
+
+    @Override
+    public void visit(WasmInt31Get expression) {
+        expression.getValue().acceptVisitor(this);
+        expression.setValue(mapper.apply(expression.getValue()));
+    }
 }

core/src/main/java/org/teavm/backend/wasm/model/expression/WasmTest.java

@@ -0,0 +1,64 @@
+/*
+ *  Copyright 2024 Alexey Andreev.
+ *
+ *  Licensed under the Apache License, Version 2.0 (the "License");
+ *  you may not use this file except in compliance with the License.
+ *  You may obtain a copy of the License at
+ *
+ *       http://www.apache.org/licenses/LICENSE-2.0
+ *
+ *  Unless required by applicable law or agreed to in writing, software
+ *  distributed under the License is distributed on an "AS IS" BASIS,
+ *  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ *  See the License for the specific language governing permissions and
+ *  limitations under the License.
+ */
+package org.teavm.backend.wasm.model.expression;
+
+import java.util.Objects;
+import org.teavm.backend.wasm.model.WasmType;
+
+public class WasmTest extends WasmExpression {
+    private WasmExpression value;
+    private WasmType.Reference testType;
+    private boolean nullable;
+
+    public WasmTest(WasmExpression value, WasmType.Reference testType) {
+        this(value, testType, true);
+    }
+
+    public WasmTest(WasmExpression value, WasmType.Reference testType, boolean nullable) {
+        this.value = Objects.requireNonNull(value);
+        this.testType = Objects.requireNonNull(testType);
+        this.nullable = nullable;
+    }
+
+    public WasmExpression getValue() {
+        return value;
+    }
+
+    public void setValue(WasmExpression value) {
+        this.value = Objects.requireNonNull(value);
+    }
+
+    public WasmType.Reference getTestType() {
+        return testType;
+    }
+
+    public void setTestType(WasmType.Reference testType) {
+        this.testType = Objects.requireNonNull(testType);
+    }
+
+    public boolean isNullable() {
+        return nullable;
+    }
+
+    public void setNullable(boolean nullable) {
+        this.nullable = nullable;
+    }
+
+    @Override
+    public void acceptVisitor(WasmExpressionVisitor visitor) {
+        visitor.visit(this);
+    }
+}

core/src/main/java/org/teavm/backend/wasm/optimization/UnusedTypeElimination.java

@@ -41,6 +41,7 @@ import org.teavm.backend.wasm.model.expression.WasmStructGet;
 import org.teavm.backend.wasm.model.expression.WasmStructNew;
 import org.teavm.backend.wasm.model.expression.WasmStructNewDefault;
 import org.teavm.backend.wasm.model.expression.WasmStructSet;
+import org.teavm.backend.wasm.model.expression.WasmTest;
 
 public class UnusedTypeElimination {
     private WasmModule module;
@@ -103,6 +104,11 @@ public class UnusedTypeElimination {
             use(expression.getTargetType());
         }
 
+        @Override
+        public void visit(WasmTest expression) {
+            super.visit(expression);
+            use(expression.getTestType());
+        }
 
         @Override
         public void visit(WasmArrayGet expression) {

core/src/main/java/org/teavm/backend/wasm/parser/CodeListener.java

@@ -135,7 +135,10 @@ public interface CodeListener {
     default void nullConstant(WasmHollowType.Reference type) {
     }
 
-    default void cast(WasmHollowType.Reference type) {
+    default void cast(WasmHollowType.Reference type, boolean nullable) {
+    }
+
+    default void test(WasmHollowType.Reference type, boolean nullable) {
     }
 
     default void structNew(int typeIndex) {
@@ -173,4 +176,10 @@ public interface CodeListener {
 
     default void functionReference(int functionIndex) {
     }
+
+    default void int31Reference() {
+    }
+
+    default void int31Get(WasmSignedType signedType) {
+    }
 }

core/src/main/java/org/teavm/backend/wasm/parser/CodeSectionParser.java

@@ -727,8 +727,31 @@ public class CodeSectionParser {
                 codeListener.arrayCopy(readLEB(), readLEB());
                 return true;
 
+            case 20:
+                codeListener.test(readHeapType(), false);
+                return true;
+
+            case 21:
+                codeListener.test(readHeapType(), true);
+                return true;
+
+            case 22:
+                codeListener.cast(readHeapType(), false);
+                return true;
+
             case 23:
-                codeListener.cast(readHeapType());
+                codeListener.cast(readHeapType(), true);
+                return true;
+
+            case 28:
+                codeListener.int31Reference();
+                return true;
+
+            case 29:
+                codeListener.int31Get(WasmSignedType.SIGNED);
+                return true;
+            case 30:
+                codeListener.int31Get(WasmSignedType.UNSIGNED);
                 return true;
 
             default:
@@ -868,6 +891,8 @@ public class CodeSectionParser {
                 return WasmHollowType.Reference.EXTERN;
             case 0x6E:
                 return WasmHollowType.Reference.ANY;
+            case 0x6C:
+                return WasmHollowType.Reference.I31;
             case 0x6B:
                 return WasmHollowType.Reference.STRUCT;
             case 0x6A:

core/src/main/java/org/teavm/backend/wasm/parser/WasmHollowType.java

@@ -61,6 +61,7 @@ public class WasmHollowType {
         public static final SpecialReference EXTERN = new SpecialReference(WasmType.SpecialReferenceKind.EXTERN);
         public static final SpecialReference STRUCT = new SpecialReference(WasmType.SpecialReferenceKind.STRUCT);
         public static final SpecialReference ARRAY = new SpecialReference(WasmType.SpecialReferenceKind.ARRAY);
+        public static final SpecialReference I31 = new SpecialReference(WasmType.SpecialReferenceKind.I31);
     }
 
     public static final class CompositeReference extends WasmHollowType.Reference {

core/src/main/java/org/teavm/backend/wasm/render/WasmBinaryRenderingVisitor.java

@@ -54,6 +54,8 @@ import org.teavm.backend.wasm.model.expression.WasmFunctionReference;
 import org.teavm.backend.wasm.model.expression.WasmGetGlobal;
 import org.teavm.backend.wasm.model.expression.WasmGetLocal;
 import org.teavm.backend.wasm.model.expression.WasmIndirectCall;
+import org.teavm.backend.wasm.model.expression.WasmInt31Get;
+import org.teavm.backend.wasm.model.expression.WasmInt31Reference;
 import org.teavm.backend.wasm.model.expression.WasmInt32Constant;
 import org.teavm.backend.wasm.model.expression.WasmInt64Constant;
 import org.teavm.backend.wasm.model.expression.WasmIntBinary;
@@ -68,6 +70,7 @@ import org.teavm.backend.wasm.model.expression.WasmReferencesEqual;
 import org.teavm.backend.wasm.model.expression.WasmReturn;
 import org.teavm.backend.wasm.model.expression.WasmSetGlobal;
 import org.teavm.backend.wasm.model.expression.WasmSetLocal;
+import org.teavm.backend.wasm.model.expression.WasmSignedType;
 import org.teavm.backend.wasm.model.expression.WasmStoreFloat32;
 import org.teavm.backend.wasm.model.expression.WasmStoreFloat64;
 import org.teavm.backend.wasm.model.expression.WasmStoreInt32;
@@ -77,6 +80,7 @@ import org.teavm.backend.wasm.model.expression.WasmStructNew;
 import org.teavm.backend.wasm.model.expression.WasmStructNewDefault;
 import org.teavm.backend.wasm.model.expression.WasmStructSet;
 import org.teavm.backend.wasm.model.expression.WasmSwitch;
+import org.teavm.backend.wasm.model.expression.WasmTest;
 import org.teavm.backend.wasm.model.expression.WasmThrow;
 import org.teavm.backend.wasm.model.expression.WasmTry;
 import org.teavm.backend.wasm.model.expression.WasmUnreachable;
@@ -1071,11 +1075,21 @@ class WasmBinaryRenderingVisitor implements WasmExpressionVisitor {
         pushLocation(expression);
         expression.getValue().acceptVisitor(this);
         writer.writeByte(0xfb);
-        writer.writeByte(23);
+        writer.writeByte(expression.isNullable() ? 23 : 22);
         writer.writeHeapType(expression.getTargetType(), module);
         popLocation();
     }
 
+    @Override
+    public void visit(WasmTest expression) {
+        pushLocation(expression);
+        expression.getValue().acceptVisitor(this);
+        writer.writeByte(0xfb);
+        writer.writeByte(expression.isNullable() ? 21 : 20);
+        writer.writeHeapType(expression.getTestType(), module);
+        popLocation();
+    }
+
     @Override
     public void visit(WasmStructNew expression) {
         pushLocation(expression);
@@ -1207,6 +1221,24 @@ class WasmBinaryRenderingVisitor implements WasmExpressionVisitor {
         popLocation();
     }
 
+    @Override
+    public void visit(WasmInt31Reference expression) {
+        pushLocation(expression);
+        expression.getValue().acceptVisitor(this);
+        writer.writeByte(0xfb);
+        writer.writeByte(28);
+        popLocation();
+    }
+
+    @Override
+    public void visit(WasmInt31Get expression) {
+        pushLocation(expression);
+        expression.getValue().acceptVisitor(this);
+        writer.writeByte(0xfb);
+        writer.writeByte(expression.getSignedType() == WasmSignedType.SIGNED ? 29 : 30);
+        popLocation();
+    }
+
     private int alignment(int value) {
         return 31 - Integer.numberOfLeadingZeros(Math.max(1, value));
     }

core/src/main/java/org/teavm/backend/wasm/render/WasmBinaryWriter.java

@@ -73,6 +73,9 @@ public class WasmBinaryWriter {
             case ARRAY:
                 writeByte(0x6a);
                 break;
+            case I31:
+                writeByte(0x6c);
+                break;
         }
     }
 

core/src/main/java/org/teavm/backend/wasm/render/WasmCRenderingVisitor.java

@@ -54,6 +54,8 @@ import org.teavm.backend.wasm.model.expression.WasmFunctionReference;
 import org.teavm.backend.wasm.model.expression.WasmGetGlobal;
 import org.teavm.backend.wasm.model.expression.WasmGetLocal;
 import org.teavm.backend.wasm.model.expression.WasmIndirectCall;
+import org.teavm.backend.wasm.model.expression.WasmInt31Get;
+import org.teavm.backend.wasm.model.expression.WasmInt31Reference;
 import org.teavm.backend.wasm.model.expression.WasmInt32Constant;
 import org.teavm.backend.wasm.model.expression.WasmInt64Constant;
 import org.teavm.backend.wasm.model.expression.WasmIntBinary;
@@ -78,6 +80,7 @@ import org.teavm.backend.wasm.model.expression.WasmStructNew;
 import org.teavm.backend.wasm.model.expression.WasmStructNewDefault;
 import org.teavm.backend.wasm.model.expression.WasmStructSet;
 import org.teavm.backend.wasm.model.expression.WasmSwitch;
+import org.teavm.backend.wasm.model.expression.WasmTest;
 import org.teavm.backend.wasm.model.expression.WasmThrow;
 import org.teavm.backend.wasm.model.expression.WasmTry;
 import org.teavm.backend.wasm.model.expression.WasmUnreachable;
@@ -1170,6 +1173,11 @@ class WasmCRenderingVisitor implements WasmExpressionVisitor {
         unsupported();
     }
 
+    @Override
+    public void visit(WasmTest expression) {
+        unsupported();
+    }
+
     @Override
     public void visit(WasmStructNew expression) {
         unsupported();
@@ -1220,6 +1228,16 @@ class WasmCRenderingVisitor implements WasmExpressionVisitor {
         unsupported();
     }
 
+    @Override
+    public void visit(WasmInt31Reference expression) {
+        unsupported();
+    }
+
+    @Override
+    public void visit(WasmInt31Get expression) {
+        unsupported();
+    }
+
     private void unsupported() {
         value = new CExpression("/* unsupported */");
     }

core/src/main/java/org/teavm/backend/wasm/render/WasmRenderingVisitor.java

@@ -53,6 +53,8 @@ import org.teavm.backend.wasm.model.expression.WasmFunctionReference;
 import org.teavm.backend.wasm.model.expression.WasmGetGlobal;
 import org.teavm.backend.wasm.model.expression.WasmGetLocal;
 import org.teavm.backend.wasm.model.expression.WasmIndirectCall;
+import org.teavm.backend.wasm.model.expression.WasmInt31Get;
+import org.teavm.backend.wasm.model.expression.WasmInt31Reference;
 import org.teavm.backend.wasm.model.expression.WasmInt32Constant;
 import org.teavm.backend.wasm.model.expression.WasmInt64Constant;
 import org.teavm.backend.wasm.model.expression.WasmIntBinary;
@@ -70,6 +72,7 @@ import org.teavm.backend.wasm.model.expression.WasmReferencesEqual;
 import org.teavm.backend.wasm.model.expression.WasmReturn;
 import org.teavm.backend.wasm.model.expression.WasmSetGlobal;
 import org.teavm.backend.wasm.model.expression.WasmSetLocal;
+import org.teavm.backend.wasm.model.expression.WasmSignedType;
 import org.teavm.backend.wasm.model.expression.WasmStoreFloat32;
 import org.teavm.backend.wasm.model.expression.WasmStoreFloat64;
 import org.teavm.backend.wasm.model.expression.WasmStoreInt32;
@@ -79,6 +82,7 @@ import org.teavm.backend.wasm.model.expression.WasmStructNew;
 import org.teavm.backend.wasm.model.expression.WasmStructNewDefault;
 import org.teavm.backend.wasm.model.expression.WasmStructSet;
 import org.teavm.backend.wasm.model.expression.WasmSwitch;
+import org.teavm.backend.wasm.model.expression.WasmTest;
 import org.teavm.backend.wasm.model.expression.WasmThrow;
 import org.teavm.backend.wasm.model.expression.WasmTry;
 import org.teavm.backend.wasm.model.expression.WasmUnreachable;
@@ -700,6 +704,13 @@ class WasmRenderingVisitor implements WasmExpressionVisitor {
         close();
     }
 
+    @Override
+    public void visit(WasmTest expression) {
+        open().append("ref.test ").append(type(expression.getTestType()));
+        line(expression.getValue());
+        close();
+    }
+
     @Override
     public void visit(WasmStructNew expression) {
         open().append("struct.new ");
@@ -811,6 +822,20 @@ class WasmRenderingVisitor implements WasmExpressionVisitor {
         close();
     }
 
+    @Override
+    public void visit(WasmInt31Reference expression) {
+        open().append("ref.i31 ");
+        line(expression.getValue());
+        close();
+    }
+
+    @Override
+    public void visit(WasmInt31Get expression) {
+        open().append("i31.get_" + (expression.getSignedType() == WasmSignedType.SIGNED ? "s" : "u"));
+        line(expression.getValue());
+        close();
+    }
+
     private String type(WasmType type) {
         if (type instanceof WasmType.Number) {
             return type(((WasmType.Number) type).number);
@@ -826,6 +851,8 @@ class WasmRenderingVisitor implements WasmExpressionVisitor {
                     return "funcref";
                 case ARRAY:
                     return "arrayref";
+                case I31:
+                    return "i31ref";
                 default:
                     throw new IllegalArgumentException();
             }

core/src/main/java/org/teavm/backend/wasm/render/WasmTypeInference.java

@@ -42,6 +42,8 @@ import org.teavm.backend.wasm.model.expression.WasmFunctionReference;
 import org.teavm.backend.wasm.model.expression.WasmGetGlobal;
 import org.teavm.backend.wasm.model.expression.WasmGetLocal;
 import org.teavm.backend.wasm.model.expression.WasmIndirectCall;
+import org.teavm.backend.wasm.model.expression.WasmInt31Get;
+import org.teavm.backend.wasm.model.expression.WasmInt31Reference;
 import org.teavm.backend.wasm.model.expression.WasmInt32Constant;
 import org.teavm.backend.wasm.model.expression.WasmInt64Constant;
 import org.teavm.backend.wasm.model.expression.WasmIntBinary;
@@ -66,6 +68,7 @@ import org.teavm.backend.wasm.model.expression.WasmStructNew;
 import org.teavm.backend.wasm.model.expression.WasmStructNewDefault;
 import org.teavm.backend.wasm.model.expression.WasmStructSet;
 import org.teavm.backend.wasm.model.expression.WasmSwitch;
+import org.teavm.backend.wasm.model.expression.WasmTest;
 import org.teavm.backend.wasm.model.expression.WasmThrow;
 import org.teavm.backend.wasm.model.expression.WasmTry;
 import org.teavm.backend.wasm.model.expression.WasmUnreachable;
@@ -278,6 +281,11 @@ public class WasmTypeInference implements WasmExpressionVisitor {
         result = expression.getTargetType();
     }
 
+    @Override
+    public void visit(WasmTest expression) {
+        result = WasmType.INT32;
+    }
+
     @Override
     public void visit(WasmStructNew expression) {
         result = expression.getType().getReference();
@@ -328,6 +336,16 @@ public class WasmTypeInference implements WasmExpressionVisitor {
         result = expression.getFunction().getType().getReference();
     }
 
+    @Override
+    public void visit(WasmInt31Get expression) {
+        result = WasmType.INT32;
+    }
+
+    @Override
+    public void visit(WasmInt31Reference expression) {
+        result = WasmType.Reference.I31;
+    }
+
     private static WasmType map(WasmIntType type) {
         switch (type) {
             case INT32:

core/src/main/java/org/teavm/backend/wasm/runtime/WasmGCSupport.java

@@ -18,6 +18,8 @@ package org.teavm.backend.wasm.runtime;
 import org.teavm.interop.Import;
 
 public class WasmGCSupport {
+    private static int lastObjectId = 1831433054;
+
     private WasmGCSupport() {
     }
 
@@ -37,6 +39,15 @@ public class WasmGCSupport {
         return new CloneNotSupportedException();
     }
 
+    public static int nextObjectId() {
+        var x = lastObjectId;
+        x ^= x << 13;
+        x ^= x >>> 17;
+        x ^= x << 5;
+        lastObjectId = x;
+        return x;
+    }
+
     @Import(name = "putcharStdout")
     public static native void putCharStdout(char c);
 

core/src/main/java/org/teavm/backend/wasm/transformation/gc/BaseClassesTransformation.java

@@ -16,13 +16,29 @@
 package org.teavm.backend.wasm.transformation.gc;
 
 import org.teavm.backend.wasm.runtime.WasmGCSupport;
+import org.teavm.model.AccessLevel;
 import org.teavm.model.ClassHolder;
 import org.teavm.model.ClassHolderTransformer;
 import org.teavm.model.ClassHolderTransformerContext;
 import org.teavm.model.ElementModifier;
+import org.teavm.model.FieldReference;
+import org.teavm.model.MethodHolder;
+import org.teavm.model.MethodReference;
+import org.teavm.model.Program;
+import org.teavm.model.ValueType;
 import org.teavm.model.emit.ProgramEmitter;
+import org.teavm.model.instructions.GetFieldInstruction;
+import org.teavm.model.instructions.InvocationType;
+import org.teavm.model.instructions.InvokeInstruction;
+import org.teavm.model.instructions.PutFieldInstruction;
 
 public class BaseClassesTransformation implements ClassHolderTransformer {
+    private static final MethodReference GET_MONITOR = new MethodReference(Object.class.getName(),
+            "getMonitor", ValueType.object("java.lang.Object$Monitor"));
+    private static final MethodReference SET_MONITOR = new MethodReference(Object.class.getName(),
+            "setMonitor", ValueType.object("java.lang.Object$Monitor"), ValueType.VOID);
+    private static final FieldReference MONITOR = new FieldReference(Object.class.getName(), "monitor");
+
     @Override
     public void transformClass(ClassHolder cls, ClassHolderTransformerContext context) {
         if (cls.getName().equals("java.lang.Object")) {
@@ -37,8 +53,22 @@ public class BaseClassesTransformation implements ClassHolderTransformer {
                         em.invoke(WasmGCSupport.class, "cnse", CloneNotSupportedException.class).raise();
                         break;
                     }
+                    default:
+                        if (method.getProgram() != null) {
+                            transformMonitorFieldAccess(method.getProgram());
+                        }
+                        break;
                 }
             }
+            var getMonitorMethod = new MethodHolder(GET_MONITOR.getDescriptor());
+            getMonitorMethod.setLevel(AccessLevel.PRIVATE);
+            getMonitorMethod.getModifiers().add(ElementModifier.NATIVE);
+            cls.addMethod(getMonitorMethod);
+
+            var setMonitorMethod = new MethodHolder(SET_MONITOR.getDescriptor());
+            setMonitorMethod.setLevel(AccessLevel.PRIVATE);
+            setMonitorMethod.getModifiers().add(ElementModifier.NATIVE);
+            cls.addMethod(setMonitorMethod);
         } else if (cls.getName().equals("java.lang.Class")) {
             for (var method : cls.getMethods()) {
                 switch (method.getName()) {
@@ -49,6 +79,45 @@ public class BaseClassesTransformation implements ClassHolderTransformer {
                         break;
                 }
             }
+        } else if (cls.getName().equals("java.lang.System")) {
+            for (var method : cls.getMethods()) {
+                switch (method.getName()) {
+                    case "arraycopy":
+                        method.setProgram(null);
+                        method.getModifiers().add(ElementModifier.NATIVE);
+                        break;
+                }
+            }
+        }
+    }
+
+    private void transformMonitorFieldAccess(Program program) {
+        for (var block : program.getBasicBlocks()) {
+            for (var instruction : block) {
+                if (instruction instanceof GetFieldInstruction) {
+                    var getField = (GetFieldInstruction) instruction;
+                    if (getField.getField().equals(MONITOR)) {
+                        var invocation = new InvokeInstruction();
+                        invocation.setType(InvocationType.SPECIAL);
+                        invocation.setInstance(getField.getInstance());
+                        invocation.setMethod(GET_MONITOR);
+                        invocation.setReceiver(getField.getReceiver());
+                        invocation.setLocation(getField.getLocation());
+                        getField.replace(invocation);
+                    }
+                } else if (instruction instanceof PutFieldInstruction) {
+                    var putField = (PutFieldInstruction) instruction;
+                    if (putField.getField().equals(MONITOR)) {
+                        var invocation = new InvokeInstruction();
+                        invocation.setType(InvocationType.SPECIAL);
+                        invocation.setInstance(putField.getInstance());
+                        invocation.setMethod(SET_MONITOR);
+                        invocation.setArguments(putField.getValue());
+                        invocation.setLocation(putField.getLocation());
+                        putField.replace(invocation);
+                    }
+                }
+            }
         }
     }
 }

core/src/main/java/org/teavm/model/analysis/BaseTypeInference.java

@@ -291,7 +291,7 @@ public abstract class BaseTypeInference<T> {
 
         @Override
         public void visit(NullConstantInstruction insn) {
-            types[insn.getReceiver().getIndex()] = nullType();
+            type(insn.getReceiver(), nullType());
         }
 
         @Override
@@ -454,6 +454,10 @@ public abstract class BaseTypeInference<T> {
             if (target != null) {
                 var t = mapType(type);
                 if (t != null) {
+                    if (types[target.getIndex()] != null) {
+                        //noinspection unchecked
+                        t = merge((T) types[target.getIndex()], t);
+                    }
                     types[target.getIndex()] = t;
                 }
             }
@@ -461,6 +465,10 @@ public abstract class BaseTypeInference<T> {
 
         void type(Variable target, T type) {
             if (target != null && type != null) {
+                if (types[target.getIndex()] != null) {
+                    //noinspection unchecked
+                    type = merge((T) types[target.getIndex()], type);
+                }
                 types[target.getIndex()] = type;
             }
         }

core/src/main/java/org/teavm/vm/TeaVM.java

@@ -388,7 +388,9 @@ public class TeaVM implements TeaVMHost, ServiceRepository {
             return !cancelled;
         });
         target.contributeDependencies(dependencyAnalyzer);
-        dependencyAnalyzer.addDependencyListener(new StdlibDependencyListener());
+        if (target.needsSystemArrayCopyOptimization()) {
+            dependencyAnalyzer.addDependencyListener(new StdlibDependencyListener());
+        }
         dependencyAnalyzer.processDependencies();
         if (wasCancelled() || !diagnostics.getSevereProblems().isEmpty()) {
             return;