Eliminate unnecessary return statements

core/src/main/java/org/teavm/ast/AbstractStatementVisitor.java

@@ -0,0 +1,78 @@
+/*
+ *  Copyright 2017 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.ast;
+
+public class AbstractStatementVisitor implements StatementVisitor {
+    @Override
+    public void visit(AssignmentStatement statement) {
+    }
+
+    @Override
+    public void visit(SequentialStatement statement) {
+    }
+
+    @Override
+    public void visit(ConditionalStatement statement) {
+    }
+
+    @Override
+    public void visit(SwitchStatement statement) {
+    }
+
+    @Override
+    public void visit(WhileStatement statement) {
+    }
+
+    @Override
+    public void visit(BlockStatement statement) {
+    }
+
+    @Override
+    public void visit(BreakStatement statement) {
+    }
+
+    @Override
+    public void visit(ContinueStatement statement) {
+    }
+
+    @Override
+    public void visit(ReturnStatement statement) {
+    }
+
+    @Override
+    public void visit(ThrowStatement statement) {
+    }
+
+    @Override
+    public void visit(InitClassStatement statement) {
+    }
+
+    @Override
+    public void visit(TryCatchStatement statement) {
+    }
+
+    @Override
+    public void visit(GotoPartStatement statement) {
+    }
+
+    @Override
+    public void visit(MonitorEnterStatement statement) {
+    }
+
+    @Override
+    public void visit(MonitorExitStatement statement) {
+    }
+}

core/src/main/java/org/teavm/ast/StatementVisitor.java

@@ -15,10 +15,6 @@
  */
 package org.teavm.ast;
 
-/**
- *
- * @author Alexey Andreev
- */
 public interface StatementVisitor {
     void visit(AssignmentStatement statement);
 

core/src/main/java/org/teavm/ast/optimization/Optimizer.java

@@ -47,8 +47,8 @@ public class Optimizer {
         method.getVariables().clear();
         method.getVariables().addAll(unusedEliminator.getReorderedVariables());
 
-        RedundantLabelEliminator labelEliminator = new RedundantLabelEliminator();
-        method.getBody().acceptVisitor(labelEliminator);
+        method.getBody().acceptVisitor(new RedundantLabelEliminator());
+        method.getBody().acceptVisitor(new RedundantReturnElimination());
 
         for (int i = 0; i < method.getVariables().size(); ++i) {
             method.getVariables().get(i).setIndex(i);
@@ -84,9 +84,12 @@ public class Optimizer {
         method.getVariables().addAll(unusedEliminator.getReorderedVariables());
 
         RedundantLabelEliminator labelEliminator = new RedundantLabelEliminator();
+        RedundantReturnElimination returnElimination = new RedundantReturnElimination();
         for (AsyncMethodPart part : method.getBody()) {
             part.getStatement().acceptVisitor(labelEliminator);
+            part.getStatement().acceptVisitor(returnElimination);
         }
+
         for (int i = 0; i < method.getVariables().size(); ++i) {
             method.getVariables().get(i).setIndex(i);
         }

core/src/main/java/org/teavm/ast/optimization/RedundantReturnElimination.java

@@ -0,0 +1,71 @@
+/*
+ *  Copyright 2017 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.ast.optimization;
+
+import java.util.List;
+import org.teavm.ast.AbstractStatementVisitor;
+import org.teavm.ast.BlockStatement;
+import org.teavm.ast.ConditionalStatement;
+import org.teavm.ast.ReturnStatement;
+import org.teavm.ast.SequentialStatement;
+import org.teavm.ast.Statement;
+import org.teavm.ast.SwitchClause;
+import org.teavm.ast.SwitchStatement;
+import org.teavm.ast.TryCatchStatement;
+
+class RedundantReturnElimination extends AbstractStatementVisitor {
+    @Override
+    public void visit(SequentialStatement statement) {
+        handleList(statement.getSequence());
+    }
+
+    @Override
+    public void visit(ConditionalStatement statement) {
+        handleList(statement.getConsequent());
+        handleList(statement.getAlternative());
+    }
+
+    @Override
+    public void visit(SwitchStatement statement) {
+        handleList(statement.getDefaultClause());
+        for (SwitchClause clause : statement.getClauses()) {
+            handleList(clause.getBody());
+        }
+    }
+
+    @Override
+    public void visit(BlockStatement statement) {
+        handleList(statement.getBody());
+    }
+
+    @Override
+    public void visit(TryCatchStatement statement) {
+        handleList(statement.getProtectedBody());
+        handleList(statement.getHandler());
+    }
+
+    private void handleList(List<Statement> statements) {
+        if (statements.isEmpty()) {
+            return;
+        }
+        Statement last = statements.get(statements.size() - 1);
+        if (last instanceof ReturnStatement && ((ReturnStatement) last).getResult() == null) {
+            statements.remove(statements.size() - 1);
+        } else {
+            last.acceptVisitor(this);
+        }
+    }
+}