Add a placeholder for jumps instructions to better inspect the stack.

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

@@ -110,7 +110,9 @@ class BranchManger {
      *            the compare instruction
      */
     void addIfOperator( int startPosition, int offset, int lineNumber, WasmNumericInstruction instr ) {
-        allParsedOperations.add( new IfParsedBlock( startPosition, offset, lineNumber, instr ) );
+        JumpInstruction jump = new JumpInstruction( startPosition + offset, 1, startPosition, lineNumber );
+        instructions.add( jump );
+        allParsedOperations.add( new IfParsedBlock( startPosition, offset, lineNumber, instr, jump ) );
     }
 
     /**
@@ -299,11 +301,13 @@ class BranchManger {
      *            the not consumed operations in the parent branch
      */
     private void calculateIf( BranchNode parent, IfParsedBlock startBlock, List<ParsedBlock> parsedOperations ) {
+        instructions.remove( startBlock.jump );
         IfPositions positions = searchElsePosition( startBlock, parsedOperations );
 
         BranchNode main = parent;
         for( int i = 0; i < positions.ifCount; i++ ) {
             IfParsedBlock parsedBlock = (IfParsedBlock)parsedOperations.remove( 0 );
+            instructions.remove( parsedBlock.jump );
             if( startBlock.endPosition < positions.thenPos || startBlock.endPosition == positions.elsePos ) {
                 // AND concatenation (&& operator)
                 int pos = parsedBlock.startPosition + 1; 
@@ -988,6 +992,8 @@ class BranchManger {
 
         private WasmNumericInstruction instr;
 
+        private JumpInstruction        jump;
+
         /**
          * Create new instance
          * 
@@ -1000,9 +1006,10 @@ class BranchManger {
          * @param instr
          *            the compare instruction
          */
-        private IfParsedBlock( int startPosition, int offset, int lineNumber, WasmNumericInstruction instr ) {
+        private IfParsedBlock( int startPosition, int offset, int lineNumber, WasmNumericInstruction instr, JumpInstruction jump ) {
             super( JavaBlockOperator.IF, startPosition, offset, startPosition + 3, lineNumber );
             this.instr = instr;
+            this.jump = jump;
         }
 
         /**

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

@@ -521,7 +521,7 @@ class JavaMethodWasmCodeBuilder extends WasmCodeBuilder {
                     case 167: // goto
                         int offset = byteCode.readShort();
                         branchManager.addGotoOperator( codePos, offset, byteCode.getCodePosition(), lineNumber );
-                        addNopInstruction( codePos, lineNumber ); // marker of the line number for the branch manager
+                        addJumpPlaceholder( codePos + offset, 0, codePos, lineNumber ); // marker of the line number for the branch manager
                         break;
                     case 168: // jsr
                     case 169: // ret
@@ -891,9 +891,8 @@ class JavaMethodWasmCodeBuilder extends WasmCodeBuilder {
                 throw new WasmException( "Unexpected compare sub operation: " + nextOp, -1 );
         }
         int offset = byteCode.readShort();
-        WasmNumericInstruction compare = new WasmNumericInstruction( numOp, valueType, codePos, lineNumber );
+        WasmNumericInstruction compare = addNumericInstruction( numOp, valueType, codePos, lineNumber );
         branchManager.addIfOperator( codePos, offset, byteCode.getLineNumber(), compare );
-        getInstructions().add( compare );
     }
 
 }

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

@@ -0,0 +1,93 @@
+/*
+   Copyright 2020 Volker Berlin (i-net software)
+
+   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 de.inetsoftware.jwebassembly.module;
+
+import java.io.IOException;
+
+import javax.annotation.Nonnull;
+
+import de.inetsoftware.jwebassembly.wasm.AnyType;
+
+/**
+ * Placeholder for a jump to inspect the stack. It is like a nop operation.
+ * 
+ * @author Volker Berlin
+ *
+ */
+class JumpInstruction extends WasmInstruction {
+
+    private int jumpPos;
+
+    private int popCount;
+
+    /**
+     * Create an instance of a nop instruction
+     * 
+     * @param jumpPos
+     *            the position of the jump
+     * @param popCount
+     *            the the count of values that are removed from the stack.
+     * @param javaCodePos
+     *            the code position/offset in the Java method
+     * @param lineNumber
+     *            the line number in the Java source code
+     */
+    JumpInstruction( int jumpPos, int popCount, int javaCodePos, int lineNumber ) {
+        super( javaCodePos, lineNumber );
+        this.jumpPos = jumpPos;
+        this.popCount = popCount;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    Type getType() {
+        return Type.Jump;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    public void writeTo( @Nonnull ModuleWriter writer ) throws IOException {
+        // nothing
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    AnyType getPushValueType() {
+        return null;
+    }
+
+    /**
+     * {@inheritDoc}
+     */
+    @Override
+    int getPopCount() {
+        return popCount;
+    }
+
+    /**
+     * Get the jump position
+     * 
+     * @return the position
+     */
+    int getJumpPosition() {
+        return jumpPos;
+    }
+}

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

@@ -598,6 +598,22 @@ public abstract class WasmCodeBuilder {
         instructions.add( new WasmNopInstruction( javaCodePos, lineNumber ) );
     }
 
+    /**
+     * Add a Jump instruction for later stack inspection
+     * 
+     * @param jumpPos
+     *            the position of the jump
+     * @param popCount
+     *            the the count of values that are removed from the stack.
+     * @param javaCodePos
+     *            the code position/offset in the Java method
+     * @param lineNumber
+     *            the line number in the Java source code
+     */
+    protected void addJumpPlaceholder( int jumpPos, int popCount, int javaCodePos, int lineNumber ) {
+        instructions.add( new JumpInstruction( jumpPos, popCount, javaCodePos, lineNumber ) );
+    }
+
     /**
      * Get a non GC polyfill function.
      * @param name the function name

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

@@ -35,7 +35,7 @@ abstract class WasmInstruction {
      * Type of instruction to faster differ as with instanceof.
      */
     static enum Type {
-        Const, Convert, Local, Global, Table, Memory, Block, Numeric, Nop, Call, CallVirtual, CallInterface, Array, Struct, Dup, DupThis;
+        Const, Convert, Local, Global, Table, Memory, Block, Numeric, Nop, Jump, Call, CallVirtual, CallInterface, Array, Struct, Dup, DupThis;
     }
 
     private int       javaCodePos;