duplicate the this on stack before a virtual method call invoke

src/de/inetsoftware/jwebassembly/binary/BinaryModuleWriter.java

@@ -1018,8 +1018,13 @@ public class BinaryModuleWriter extends ModuleWriter implements InstructionOpcod
      * {@inheritDoc}
      */
     @Override
-    protected void writeVirtualFunctionCall( FunctionName name, AnyType type, int virtualFunctionIdx ) throws IOException {
+    protected void writeVirtualFunctionCall( FunctionName name, AnyType type, int virtualFunctionIdx, int tempVarIdx ) throws IOException {
         callIndirect = true;
+
+        // duplicate this on the stack
+        writeLocal( VariableOperator.tee, tempVarIdx );
+        writeLocal( VariableOperator.get, tempVarIdx );
+
         codeStream.writeOpCode( STRUCT_GET );
         codeStream.writeValueType( type );
         codeStream.writeVaruint32( 0 ); // vtable is ever on position 0

src/de/inetsoftware/jwebassembly/module/ModuleWriter.java

@@ -244,10 +244,12 @@ public abstract class ModuleWriter implements Closeable {
      *            the base type that should be called
      * @param virtualFunctionIdx
      *            the index of the virtual method in the object. If the value < 0 a direct call should be used.
+     * @param tempVarIdx
+     *            the index of a temporary variable of type "type" to duplicate "this"
      * @throws IOException
      *             if any I/O error occur
      */
-    protected abstract void writeVirtualFunctionCall( FunctionName name, AnyType type, int virtualFunctionIdx ) throws IOException;
+    protected abstract void writeVirtualFunctionCall( FunctionName name, AnyType type, int virtualFunctionIdx, int tempVarIdx ) throws IOException;
 
     /**
      * Write a block/branch code

src/de/inetsoftware/jwebassembly/module/WasmCallIndirectInstruction.java

@@ -30,23 +30,36 @@ import de.inetsoftware.jwebassembly.module.TypeManager.StructType;
  */
 class WasmCallIndirectInstruction extends WasmCallInstruction {
 
-    private int virtualFunctionIdx = -1;
+    private int                         virtualFunctionIdx = -1;
 
-    private StructType type;
+    private final StructType            type;
+
+    private final int                   tempVar;
+
+    private final LocaleVariableManager localVariables;
 
     /**
      * Create an instance of a function call instruction
      * 
      * @param name
      *            the function name that should be called
+     * @param type
+     *            the type with the virtual method/function
+     * @param tempVar
+     *            the slot of a temporary variable of type "type" to duplicate "this"
+     * @param localVariables
+     *            the manager for local variables to translate the Java slot of the temporary variable into wasm local
+     *            position
      * @param javaCodePos
      *            the code position/offset in the Java method
      * @param lineNumber
      *            the line number in the Java source code
      */
-    WasmCallIndirectInstruction( FunctionName name, @Nonnull StructType type, int javaCodePos, int lineNumber ) {
+    WasmCallIndirectInstruction( FunctionName name, @Nonnull StructType type, int tempVar, LocaleVariableManager localVariables, int javaCodePos, int lineNumber ) {
         super( name, javaCodePos, lineNumber );
         this.type = type;
+        this.tempVar = tempVar;
+        this.localVariables = localVariables;
     }
 
     /**
@@ -74,7 +87,8 @@ class WasmCallIndirectInstruction extends WasmCallInstruction {
         if( virtualFunctionIdx < 0 || true ) {
             super.writeTo( writer );
         } else {
-            writer.writeVirtualFunctionCall( getFunctionName(), type, virtualFunctionIdx );
+            int tempVarIdx = localVariables.get( tempVar, getCodePosition() );
+            writer.writeVirtualFunctionCall( getFunctionName(), type, virtualFunctionIdx, tempVarIdx );
         }
     }
 

src/de/inetsoftware/jwebassembly/module/WasmCodeBuilder.java

@@ -285,7 +285,8 @@ public abstract class WasmCodeBuilder {
      */
     protected void addCallVirtualInstruction( FunctionName name, int javaCodePos, int lineNumber ) {
         StructType type = types.valueOf( name.className );
-        instructions.add( new WasmCallIndirectInstruction( name, type, javaCodePos, lineNumber ) );
+        int tempVar = localVariables.getTempVariable( type, javaCodePos, javaCodePos + 1 );
+        instructions.add( new WasmCallIndirectInstruction( name, type, tempVar, localVariables, javaCodePos, lineNumber ) );
     }
 
     /**

src/de/inetsoftware/jwebassembly/text/TextModuleWriter.java

@@ -580,8 +580,13 @@ public class TextModuleWriter extends ModuleWriter {
      * {@inheritDoc}
      */
     @Override
-    protected void writeVirtualFunctionCall( FunctionName name, AnyType type, int virtualFunctionIdx ) throws IOException {
+    protected void writeVirtualFunctionCall( FunctionName name, AnyType type, int virtualFunctionIdx, int tempVarIdx ) throws IOException {
         callIndirect = true;
+
+        // duplicate this on the stack
+        writeLocal( VariableOperator.tee, tempVarIdx );
+        writeLocal( VariableOperator.get, tempVarIdx );
+
         newline( methodOutput );
         methodOutput.append( "struct.get " ).append( normalizeName( type.toString() ) ).append( " 0 ;;vtable" ); // vtable is ever on position 0
         newline( methodOutput );