wasm gc: implement branching instructions and null check instruction

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

@@ -120,10 +120,33 @@ public class DisassemblyCodeListener extends BaseDisassemblyListener implements
             case BR_IF:
                 writer.write("br_if");
                 break;
+            case BR_ON_NULL:
+                writer.write("br_on_null");
+                break;
+            case BR_ON_NON_NULL:
+                writer.write("br_on_non_null");
+                break;
         }
         writer.endLink().write(" $label_" + target).eol();
     }
 
+    @Override
+    public void castBranch(boolean success, int depth, int target, WasmHollowType.Reference sourceType,
+            WasmHollowType.Reference targetType) {
+        writer.address().startLink("start" + target);
+        if (success) {
+            writer.write("br_if_cast");
+        } else {
+            writer.write("br_if_cast_fail");
+        }
+        writer.endLink().write(" $label_" + target);
+        writer.write(" ");
+        writeType(sourceType);
+        writer.write(" ");
+        writeType(sourceType);
+        writer.eol();
+    }
+
     @Override
     public void tableBranch(int[] depths, int[] targets, int defaultDepth, int defaultTarget) {
         writer.address();
@@ -162,6 +185,9 @@ public class DisassemblyCodeListener extends BaseDisassemblyListener implements
             case ARRAY_LENGTH:
                 writer.write("array.length");
                 break;
+            case IS_NULL:
+                writer.write("ref.is_null");
+                break;
         }
         writer.eol();
     }

core/src/main/java/org/teavm/backend/wasm/generate/common/methods/BaseWasmGenerationVisitor.java

@@ -449,7 +449,7 @@ public abstract class BaseWasmGenerationVisitor implements StatementVisitor, Exp
 
     protected abstract boolean isManagedCall(MethodReference method);
 
-    private WasmExpression nullCheck(Expr value, TextLocation location) {
+    protected WasmExpression nullCheck(Expr value, TextLocation location) {
         var block = new WasmBlock(false);
         block.setLocation(location);
 

core/src/main/java/org/teavm/backend/wasm/generate/gc/classes/WasmGCSupertypeFunctionGenerator.java

@@ -35,7 +35,7 @@ import org.teavm.backend.wasm.model.expression.WasmInt32Constant;
 import org.teavm.backend.wasm.model.expression.WasmIntBinary;
 import org.teavm.backend.wasm.model.expression.WasmIntBinaryOperation;
 import org.teavm.backend.wasm.model.expression.WasmIntType;
-import org.teavm.backend.wasm.model.expression.WasmNullConstant;
+import org.teavm.backend.wasm.model.expression.WasmIsNull;
 import org.teavm.backend.wasm.model.expression.WasmReferencesEqual;
 import org.teavm.backend.wasm.model.expression.WasmReturn;
 import org.teavm.backend.wasm.model.expression.WasmSetLocal;
@@ -156,8 +156,7 @@ public class WasmGCSupertypeFunctionGenerator implements WasmGCSupertypeFunction
         var itemExpression = getClassField(new WasmGetLocal(subtypeVar), itemOffset);
         body.add(new WasmSetLocal(subtypeVar, itemExpression));
 
-        var itemTest = new WasmConditional(new WasmReferencesEqual(new WasmGetLocal(subtypeVar),
+        var itemTest = new WasmConditional(new WasmIsNull(new WasmGetLocal(subtypeVar)));
-                new WasmNullConstant(WasmType.Reference.STRUCT)));
         itemTest.setType(WasmType.INT32);
         itemTest.getThenBlock().getBody().add(new WasmInt32Constant(0));
 

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

@@ -57,6 +57,9 @@ import org.teavm.backend.wasm.model.expression.WasmGetLocal;
 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.WasmIsNull;
+import org.teavm.backend.wasm.model.expression.WasmNullBranch;
+import org.teavm.backend.wasm.model.expression.WasmNullCondition;
 import org.teavm.backend.wasm.model.expression.WasmNullConstant;
 import org.teavm.backend.wasm.model.expression.WasmReferencesEqual;
 import org.teavm.backend.wasm.model.expression.WasmSetGlobal;
@@ -232,7 +235,32 @@ public class WasmGCGenerationVisitor extends BaseWasmGenerationVisitor {
 
     @Override
     protected WasmExpression genIsNull(WasmExpression value) {
-        return new WasmReferencesEqual(value, new WasmNullConstant(WasmType.Reference.STRUCT));
+        return new WasmIsNull(value);
+    }
+
+    protected WasmExpression nullCheck(Expr value, TextLocation location) {
+        var block = new WasmBlock(false);
+        block.setLocation(location);
+
+        accept(value);
+        if (result instanceof WasmUnreachable) {
+            return result;
+        }
+        result.acceptVisitor(typeInference);
+        block.setType(typeInference.getResult());
+        var cachedValue = exprCache.create(result, typeInference.getResult(), location, block.getBody());
+
+        var check = new WasmNullBranch(WasmNullCondition.NOT_NULL, cachedValue.expr(), block);
+        check.setResult(cachedValue.expr());
+        block.getBody().add(new WasmDrop(check));
+
+        var callSiteId = generateCallSiteId(location);
+        callSiteId.generateRegister(block.getBody(), location);
+        generateThrowNPE(location, block.getBody());
+        callSiteId.generateThrow(block.getBody(), location);
+
+        cachedValue.release();
+        return block;
     }
 
     @Override

core/src/main/java/org/teavm/backend/wasm/generators/gc/ClassGenerators.java

@@ -22,8 +22,7 @@ import org.teavm.backend.wasm.model.expression.WasmCall;
 import org.teavm.backend.wasm.model.expression.WasmCallReference;
 import org.teavm.backend.wasm.model.expression.WasmConditional;
 import org.teavm.backend.wasm.model.expression.WasmGetLocal;
-import org.teavm.backend.wasm.model.expression.WasmNullConstant;
+import org.teavm.backend.wasm.model.expression.WasmIsNull;
-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.WasmStructGet;
@@ -50,8 +49,7 @@ public class ClassGenerators implements WasmGCCustomGenerator {
         function.add(thisVar);
         function.add(otherClassVar);
 
-        var conditional = new WasmConditional(new WasmReferencesEqual(new WasmGetLocal(otherClassVar),
+        var conditional = new WasmConditional(new WasmIsNull(new WasmGetLocal(otherClassVar)));
-                new WasmNullConstant(WasmType.Reference.STRUCT)));
         function.getBody().add(conditional);
         var npe = new WasmCall(context.functions().forStaticMethod(new MethodReference(WasmGCSupport.class, "npe",
                 NullPointerException.class)));

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

@@ -0,0 +1,89 @@
+/*
+ *  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 WasmCastBranch extends WasmExpression {
+    private WasmCastCondition condition;
+    private WasmExpression value;
+    private WasmType.Reference sourceType;
+    private WasmType.Reference type;
+    private WasmBlock target;
+    private WasmExpression result;
+
+    public WasmCastBranch(WasmCastCondition condition, WasmExpression value, WasmType.Reference sourceType,
+            WasmType.Reference type, WasmBlock target) {
+        this.condition = Objects.requireNonNull(condition);
+        this.value = Objects.requireNonNull(value);
+        this.type = Objects.requireNonNull(type);
+        this.target = Objects.requireNonNull(target);
+    }
+
+    public WasmCastCondition getCondition() {
+        return condition;
+    }
+
+    public void setCondition(WasmCastCondition condition) {
+        this.condition = Objects.requireNonNull(condition);
+    }
+
+    public WasmExpression getValue() {
+        return value;
+    }
+
+    public void setValue(WasmExpression value) {
+        this.value = Objects.requireNonNull(value);
+    }
+
+    public WasmType.Reference getSourceType() {
+        return sourceType;
+    }
+
+    public void setSourceType(WasmType.Reference sourceType) {
+        this.sourceType = Objects.requireNonNull(sourceType);
+    }
+
+    public WasmType.Reference getType() {
+        return type;
+    }
+
+    public void setType(WasmType.Reference type) {
+        this.type = Objects.requireNonNull(type);
+    }
+
+    public WasmBlock getTarget() {
+        return target;
+    }
+
+    public void setTarget(WasmBlock target) {
+        this.target = Objects.requireNonNull(target);
+    }
+
+    public WasmExpression getResult() {
+        return result;
+    }
+
+    public void setResult(WasmExpression result) {
+        this.result = result;
+    }
+
+    @Override
+    public void acceptVisitor(WasmExpressionVisitor visitor) {
+        visitor.visit(this);
+    }
+}

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

@@ -0,0 +1,21 @@
+/*
+ *  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;
+
+public enum WasmCastCondition {
+    SUCCESS,
+    FAILURE
+}

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

@@ -31,6 +31,22 @@ public class WasmDefaultExpressionVisitor implements WasmExpressionVisitor {
         }
     }
 
+    @Override
+    public void visit(WasmNullBranch expression) {
+        expression.getValue().acceptVisitor(this);
+        if (expression.getResult() != null) {
+            expression.getResult().acceptVisitor(this);
+        }
+    }
+
+    @Override
+    public void visit(WasmCastBranch expression) {
+        expression.getValue().acceptVisitor(this);
+        if (expression.getResult() != null) {
+            expression.getResult().acceptVisitor(this);
+        }
+    }
+
     @Override
     public void visit(WasmBreak expression) {
         if (expression.getResult() != null) {
@@ -85,6 +101,11 @@ public class WasmDefaultExpressionVisitor implements WasmExpressionVisitor {
     public void visit(WasmNullConstant expression) {
     }
 
+    @Override
+    public void visit(WasmIsNull expression) {
+        expression.getValue().acceptVisitor(this);
+    }
+
     @Override
     public void visit(WasmGetLocal expression) {
     }

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

@@ -20,6 +20,10 @@ public interface WasmExpressionVisitor {
 
     void visit(WasmBranch expression);
 
+    void visit(WasmNullBranch expression);
+
+    void visit(WasmCastBranch expression);
+
     void visit(WasmBreak expression);
 
     void visit(WasmSwitch expression);
@@ -40,6 +44,8 @@ public interface WasmExpressionVisitor {
 
     void visit(WasmNullConstant expression);
 
+    void visit(WasmIsNull expression);
+
     void visit(WasmGetLocal expression);
 
     void visit(WasmSetLocal expression);

core/src/main/java/org/teavm/backend/wasm/model/expression/WasmIsNull.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 WasmIsNull extends WasmExpression {
+    private WasmExpression value;
+
+    public WasmIsNull(WasmExpression value) {
+        this.value = Objects.requireNonNull(value);
+    }
+
+    public WasmExpression getValue() {
+        return value;
+    }
+
+    public void setValue(WasmExpression value) {
+        this.value = value;
+    }
+
+    @Override
+    public void acceptVisitor(WasmExpressionVisitor visitor) {
+        visitor.visit(this);
+    }
+}

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

@@ -0,0 +1,68 @@
+/*
+ *  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 WasmNullBranch extends WasmExpression {
+    private WasmNullCondition condition;
+    private WasmExpression value;
+    private WasmBlock target;
+    private WasmExpression result;
+
+    public WasmNullBranch(WasmNullCondition condition, WasmExpression value, WasmBlock target) {
+        this.condition = Objects.requireNonNull(condition);
+        this.value = Objects.requireNonNull(value);
+        this.target = Objects.requireNonNull(target);
+    }
+
+    public WasmNullCondition getCondition() {
+        return condition;
+    }
+
+    public void setCondition(WasmNullCondition condition) {
+        this.condition = Objects.requireNonNull(condition);
+    }
+
+    public WasmExpression getValue() {
+        return value;
+    }
+
+    public void setValue(WasmExpression value) {
+        this.value = Objects.requireNonNull(value);
+    }
+
+    public WasmBlock getTarget() {
+        return target;
+    }
+
+    public void setTarget(WasmBlock target) {
+        this.target = Objects.requireNonNull(target);
+    }
+
+    public WasmExpression getResult() {
+        return result;
+    }
+
+    public void setResult(WasmExpression result) {
+        this.result = result;
+    }
+
+    @Override
+    public void acceptVisitor(WasmExpressionVisitor visitor) {
+        visitor.visit(this);
+    }
+}

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

@@ -0,0 +1,21 @@
+/*
+ *  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;
+
+public enum WasmNullCondition {
+    NULL,
+    NOT_NULL
+}

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

@@ -55,6 +55,26 @@ public class WasmReplacingExpressionVisitor implements WasmExpressionVisitor {
         }
     }
 
+    @Override
+    public void visit(WasmNullBranch expression) {
+        expression.getValue().acceptVisitor(this);
+        expression.setValue(mapper.apply(expression.getValue()));
+        if (expression.getResult() != null) {
+            expression.getResult().acceptVisitor(this);
+            expression.setResult(mapper.apply(expression.getResult()));
+        }
+    }
+
+    @Override
+    public void visit(WasmCastBranch expression) {
+        expression.getValue().acceptVisitor(this);
+        expression.setValue(mapper.apply(expression.getValue()));
+        if (expression.getResult() != null) {
+            expression.getResult().acceptVisitor(this);
+            expression.setResult(mapper.apply(expression.getResult()));
+        }
+    }
+
     @Override
     public void visit(WasmBreak expression) {
         if (expression.getResult() != null) {
@@ -109,6 +129,12 @@ public class WasmReplacingExpressionVisitor implements WasmExpressionVisitor {
     public void visit(WasmNullConstant expression) {
     }
 
+    @Override
+    public void visit(WasmIsNull expression) {
+        expression.getValue().acceptVisitor(this);
+        expression.setValue(mapper.apply(expression.getValue()));
+    }
+
     @Override
     public void visit(WasmGetLocal expression) {
     }

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

@@ -17,5 +17,7 @@ package org.teavm.backend.wasm.parser;
 
 public enum BranchOpcode {
     BR,
-    BR_IF
+    BR_IF,
+    BR_ON_NULL,
+    BR_ON_NON_NULL
 }

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

@@ -54,6 +54,10 @@ public interface CodeListener {
     default void branch(BranchOpcode opcode, int depth, int target) {
     }
 
+    default void castBranch(boolean success, int depth, int target, WasmHollowType.Reference sourceType,
+            WasmHollowType.Reference targetType) {
+    }
+
     default void tableBranch(int[] depths, int[] targets, int defaultDepth, int defaultTarget) {
     }
 

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

@@ -591,6 +591,9 @@ public class CodeParser extends BaseSectionParser {
             case 0xD0:
                 codeListener.nullConstant(reader.readHeapType(true));
                 break;
+            case 0xD1:
+                codeListener.opcode(Opcode.IS_NULL);
+                break;
 
             case 0xD2:
                 codeListener.functionReference(readLEB());
@@ -600,6 +603,13 @@ public class CodeParser extends BaseSectionParser {
                 codeListener.opcode(Opcode.REF_EQ);
                 break;
 
+            case 0xD5:
+                parseBranch(BranchOpcode.BR_ON_NULL);
+                break;
+            case 0xD6:
+                parseBranch(BranchOpcode.BR_ON_NON_NULL);
+                break;
+
             case 0xFB:
                 return parseExtExpr2();
             case 0xFC:
@@ -702,6 +712,13 @@ public class CodeParser extends BaseSectionParser {
                 codeListener.cast(reader.readHeapType(true));
                 return true;
 
+            case 24:
+                parseCastBranch(true);
+                return true;
+            case 25:
+                parseCastBranch(false);
+                return true;
+
             case 28:
                 codeListener.int31Reference();
                 return true;
@@ -798,6 +815,15 @@ public class CodeParser extends BaseSectionParser {
         codeListener.branch(opcode, depth, target.token);
     }
 
+    private void parseCastBranch(boolean success) {
+        var depth = readLEB();
+        var target = blockStack.get(blockStack.size() - depth - 1);
+        var flags = reader.data[reader.ptr++];
+        var sourceType = reader.readHeapType((flags & 1) != 0);
+        var targetType = reader.readHeapType((flags & 2) != 0);
+        codeListener.castBranch(success, depth, target.token, sourceType, targetType);
+    }
+
     private void parseTableBranch() {
         var count = readLEB();
         var depths = new int[count];

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

@@ -21,5 +21,6 @@ public enum Opcode {
     RETURN,
     DROP,
     REF_EQ,
-    ARRAY_LENGTH
+    ARRAY_LENGTH,
+    IS_NULL
 }

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

@@ -39,6 +39,7 @@ import org.teavm.backend.wasm.model.expression.WasmBreak;
 import org.teavm.backend.wasm.model.expression.WasmCall;
 import org.teavm.backend.wasm.model.expression.WasmCallReference;
 import org.teavm.backend.wasm.model.expression.WasmCast;
+import org.teavm.backend.wasm.model.expression.WasmCastBranch;
 import org.teavm.backend.wasm.model.expression.WasmConditional;
 import org.teavm.backend.wasm.model.expression.WasmConversion;
 import org.teavm.backend.wasm.model.expression.WasmCopy;
@@ -61,11 +62,13 @@ import org.teavm.backend.wasm.model.expression.WasmInt32Constant;
 import org.teavm.backend.wasm.model.expression.WasmInt64Constant;
 import org.teavm.backend.wasm.model.expression.WasmIntBinary;
 import org.teavm.backend.wasm.model.expression.WasmIntUnary;
+import org.teavm.backend.wasm.model.expression.WasmIsNull;
 import org.teavm.backend.wasm.model.expression.WasmLoadFloat32;
 import org.teavm.backend.wasm.model.expression.WasmLoadFloat64;
 import org.teavm.backend.wasm.model.expression.WasmLoadInt32;
 import org.teavm.backend.wasm.model.expression.WasmLoadInt64;
 import org.teavm.backend.wasm.model.expression.WasmMemoryGrow;
+import org.teavm.backend.wasm.model.expression.WasmNullBranch;
 import org.teavm.backend.wasm.model.expression.WasmNullConstant;
 import org.teavm.backend.wasm.model.expression.WasmReferencesEqual;
 import org.teavm.backend.wasm.model.expression.WasmReturn;
@@ -122,6 +125,18 @@ class WasmBinaryRenderingVisitor implements WasmExpressionVisitor {
                 register(expression.getTarget());
             }
 
+            @Override
+            public void visit(WasmNullBranch expression) {
+                super.visit(expression);
+                register(expression.getTarget());
+            }
+
+            @Override
+            public void visit(WasmCastBranch expression) {
+                super.visit(expression);
+                register(expression.getTarget());
+            }
+
             @Override
             public void visit(WasmBreak expression) {
                 super.visit(expression);
@@ -186,6 +201,55 @@ class WasmBinaryRenderingVisitor implements WasmExpressionVisitor {
         popLocation();
     }
 
+    @Override
+    public void visit(WasmNullBranch expression) {
+        pushLocation(expression);
+        if (expression.getResult() != null) {
+            expression.getResult().acceptVisitor(this);
+        }
+        expression.getValue().acceptVisitor(this);
+        switch (expression.getCondition()) {
+            case NULL:
+                writer.writeByte(0xD5);
+                break;
+            case NOT_NULL:
+                writer.writeByte(0xD6);
+                break;
+        }
+        writeLabel(expression.getTarget());
+        popLocation();
+    }
+
+    @Override
+    public void visit(WasmCastBranch expression) {
+        pushLocation(expression);
+        if (expression.getResult() != null) {
+            expression.getResult().acceptVisitor(this);
+        }
+        expression.getValue().acceptVisitor(this);
+        writer.writeByte(0xFB);
+        switch (expression.getCondition()) {
+            case SUCCESS:
+                writer.writeByte(24);
+                break;
+            case FAILURE:
+                writer.writeByte(25);
+                break;
+        }
+        writeLabel(expression.getTarget());
+        var flags = 0;
+        if (expression.getSourceType().isNullable()) {
+            flags |= 1;
+        }
+        if (expression.getType().isNullable()) {
+            flags |= 2;
+        }
+        writer.writeByte(flags);
+        writer.writeHeapType(expression.getSourceType(), module);
+        writer.writeHeapType(expression.getType(), module);
+        popLocation();
+    }
+
     @Override
     public void visit(WasmBreak expression) {
         pushLocation(expression);
@@ -304,6 +368,14 @@ class WasmBinaryRenderingVisitor implements WasmExpressionVisitor {
         popLocation();
     }
 
+    @Override
+    public void visit(WasmIsNull expression) {
+        pushLocation(expression);
+        expression.getValue().acceptVisitor(this);
+        writer.writeByte(0xD1);
+        popLocation();
+    }
+
     @Override
     public void visit(WasmGetLocal expression) {
         pushLocation(expression);

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

@@ -39,6 +39,7 @@ import org.teavm.backend.wasm.model.expression.WasmBreak;
 import org.teavm.backend.wasm.model.expression.WasmCall;
 import org.teavm.backend.wasm.model.expression.WasmCallReference;
 import org.teavm.backend.wasm.model.expression.WasmCast;
+import org.teavm.backend.wasm.model.expression.WasmCastBranch;
 import org.teavm.backend.wasm.model.expression.WasmConditional;
 import org.teavm.backend.wasm.model.expression.WasmConversion;
 import org.teavm.backend.wasm.model.expression.WasmCopy;
@@ -62,11 +63,13 @@ import org.teavm.backend.wasm.model.expression.WasmInt64Constant;
 import org.teavm.backend.wasm.model.expression.WasmIntBinary;
 import org.teavm.backend.wasm.model.expression.WasmIntType;
 import org.teavm.backend.wasm.model.expression.WasmIntUnary;
+import org.teavm.backend.wasm.model.expression.WasmIsNull;
 import org.teavm.backend.wasm.model.expression.WasmLoadFloat32;
 import org.teavm.backend.wasm.model.expression.WasmLoadFloat64;
 import org.teavm.backend.wasm.model.expression.WasmLoadInt32;
 import org.teavm.backend.wasm.model.expression.WasmLoadInt64;
 import org.teavm.backend.wasm.model.expression.WasmMemoryGrow;
+import org.teavm.backend.wasm.model.expression.WasmNullBranch;
 import org.teavm.backend.wasm.model.expression.WasmNullConstant;
 import org.teavm.backend.wasm.model.expression.WasmReferencesEqual;
 import org.teavm.backend.wasm.model.expression.WasmReturn;
@@ -187,6 +190,16 @@ class WasmCRenderingVisitor implements WasmExpressionVisitor {
         value = result;
     }
 
+    @Override
+    public void visit(WasmNullBranch expression) {
+        unsupported();
+    }
+
+    @Override
+    public void visit(WasmCastBranch expression) {
+        unsupported();
+    }
+
     @Override
     public void visit(WasmBreak expression) {
         CExpression result = new CExpression();
@@ -359,6 +372,11 @@ class WasmCRenderingVisitor implements WasmExpressionVisitor {
         value = CExpression.relocatable("/* can't produce ref.null */");
     }
 
+    @Override
+    public void visit(WasmIsNull expression) {
+        unsupported();
+    }
+
     @Override
     public void visit(WasmGetLocal expression) {
         value = new CExpression(getVariableName(expression.getLocal()));

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

@@ -35,6 +35,7 @@ import org.teavm.backend.wasm.model.expression.WasmBreak;
 import org.teavm.backend.wasm.model.expression.WasmCall;
 import org.teavm.backend.wasm.model.expression.WasmCallReference;
 import org.teavm.backend.wasm.model.expression.WasmCast;
+import org.teavm.backend.wasm.model.expression.WasmCastBranch;
 import org.teavm.backend.wasm.model.expression.WasmConditional;
 import org.teavm.backend.wasm.model.expression.WasmConversion;
 import org.teavm.backend.wasm.model.expression.WasmCopy;
@@ -63,11 +64,13 @@ import org.teavm.backend.wasm.model.expression.WasmIntBinaryOperation;
 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.WasmIsNull;
 import org.teavm.backend.wasm.model.expression.WasmLoadFloat32;
 import org.teavm.backend.wasm.model.expression.WasmLoadFloat64;
 import org.teavm.backend.wasm.model.expression.WasmLoadInt32;
 import org.teavm.backend.wasm.model.expression.WasmLoadInt64;
 import org.teavm.backend.wasm.model.expression.WasmMemoryGrow;
+import org.teavm.backend.wasm.model.expression.WasmNullBranch;
 import org.teavm.backend.wasm.model.expression.WasmNullConstant;
 import org.teavm.backend.wasm.model.expression.WasmReferencesEqual;
 import org.teavm.backend.wasm.model.expression.WasmReturn;
@@ -108,6 +111,18 @@ class WasmRenderingVisitor implements WasmExpressionVisitor {
                 register(expression.getTarget());
             }
 
+            @Override
+            public void visit(WasmCastBranch expression) {
+                super.visit(expression);
+                register(expression.getTarget());
+            }
+
+            @Override
+            public void visit(WasmNullBranch expression) {
+                super.visit(expression);
+                register(expression.getTarget());
+            }
+
             @Override
             public void visit(WasmBreak expression) {
                 super.visit(expression);
@@ -219,6 +234,46 @@ class WasmRenderingVisitor implements WasmExpressionVisitor {
         close();
     }
 
+    @Override
+    public void visit(WasmNullBranch expression) {
+        String id = blockIdentifiers.get(expression.getTarget());
+        open();
+        switch (expression.getCondition()) {
+            case NULL:
+                append("br_on_null");
+                break;
+            case NOT_NULL:
+                append("br_on_non_null");
+                break;
+        }
+        append(" $" + id);
+        if (expression.getResult() != null) {
+            line(expression.getResult());
+        }
+        close();
+    }
+
+    @Override
+    public void visit(WasmCastBranch expression) {
+        String id = blockIdentifiers.get(expression.getTarget());
+        open();
+        switch (expression.getCondition()) {
+            case SUCCESS:
+                append("br_on_cast");
+                break;
+            case FAILURE:
+                append("br_on_cast_fail");
+                break;
+        }
+        append(" $").append(id);
+        append(" ").append(type(expression.getSourceType()));
+        append(" ").append(type(expression.getType()));
+        if (expression.getResult() != null) {
+            line(expression.getResult());
+        }
+        close();
+    }
+
     @Override
     public void visit(WasmBreak expression) {
         String id = blockIdentifiers.get(expression.getTarget());
@@ -300,6 +355,11 @@ class WasmRenderingVisitor implements WasmExpressionVisitor {
         open().append("ref.null " + type(expression.getType())).close();
     }
 
+    @Override
+    public void visit(WasmIsNull expression) {
+        open().append("ref.is_null").close();
+    }
+
     @Override
     public void visit(WasmGetLocal expression) {
         open().append("local.get " + asString(expression.getLocal())).close();

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

@@ -28,6 +28,7 @@ import org.teavm.backend.wasm.model.expression.WasmBreak;
 import org.teavm.backend.wasm.model.expression.WasmCall;
 import org.teavm.backend.wasm.model.expression.WasmCallReference;
 import org.teavm.backend.wasm.model.expression.WasmCast;
+import org.teavm.backend.wasm.model.expression.WasmCastBranch;
 import org.teavm.backend.wasm.model.expression.WasmConditional;
 import org.teavm.backend.wasm.model.expression.WasmConversion;
 import org.teavm.backend.wasm.model.expression.WasmCopy;
@@ -50,11 +51,13 @@ import org.teavm.backend.wasm.model.expression.WasmInt64Constant;
 import org.teavm.backend.wasm.model.expression.WasmIntBinary;
 import org.teavm.backend.wasm.model.expression.WasmIntType;
 import org.teavm.backend.wasm.model.expression.WasmIntUnary;
+import org.teavm.backend.wasm.model.expression.WasmIsNull;
 import org.teavm.backend.wasm.model.expression.WasmLoadFloat32;
 import org.teavm.backend.wasm.model.expression.WasmLoadFloat64;
 import org.teavm.backend.wasm.model.expression.WasmLoadInt32;
 import org.teavm.backend.wasm.model.expression.WasmLoadInt64;
 import org.teavm.backend.wasm.model.expression.WasmMemoryGrow;
+import org.teavm.backend.wasm.model.expression.WasmNullBranch;
 import org.teavm.backend.wasm.model.expression.WasmNullConstant;
 import org.teavm.backend.wasm.model.expression.WasmReferencesEqual;
 import org.teavm.backend.wasm.model.expression.WasmReturn;
@@ -88,7 +91,28 @@ public class WasmTypeInference implements WasmExpressionVisitor {
 
     @Override
     public void visit(WasmBranch expression) {
-        result = null;
+        if (expression.getResult() != null) {
+            expression.acceptVisitor(this);
+        }
+    }
+
+    @Override
+    public void visit(WasmNullBranch expression) {
+        if (expression.getResult() != null) {
+            expression.acceptVisitor(this);
+        }
+    }
+
+    @Override
+    public void visit(WasmCastBranch expression) {
+        switch (expression.getCondition()) {
+            case SUCCESS:
+                result = expression.getSourceType();
+                break;
+            case FAILURE:
+                result = expression.getType();
+                break;
+        }
     }
 
     @Override
@@ -186,6 +210,12 @@ public class WasmTypeInference implements WasmExpressionVisitor {
         result = expression.type;
     }
 
+
+    @Override
+    public void visit(WasmIsNull expression) {
+        result = WasmType.INT32;
+    }
+
     @Override
     public void visit(WasmCall expression) {
         var function = expression.getFunction();