Add nullness analysis

core/src/main/java/org/teavm/model/Variable.java

@@ -62,6 +62,7 @@ public class Variable implements VariableReader {
         this.debugName = debugName;
     }
 
+    @Override
     public String getLabel() {
         return label;
     }

core/src/main/java/org/teavm/model/VariableReader.java

@@ -22,5 +22,7 @@ public interface VariableReader {
 
     String getDebugName();
 
+    String getLabel();
+
     int getRegister();
 }

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

@@ -15,17 +15,75 @@
  */
 package org.teavm.model.analysis;
 
+import java.util.Arrays;
+import java.util.BitSet;
+import java.util.HashSet;
+import java.util.Set;
+import org.teavm.model.BasicBlock;
+import org.teavm.model.Instruction;
+import org.teavm.model.MethodDescriptor;
+import org.teavm.model.Phi;
 import org.teavm.model.Program;
+import org.teavm.model.TryCatchBlock;
+import org.teavm.model.TryCatchJoint;
+import org.teavm.model.Variable;
+import org.teavm.model.util.DefinitionExtractor;
+import org.teavm.model.util.InstructionVariableMapper;
+import org.teavm.model.util.PhiUpdater;
 
 public class NullnessInformation {
-    NullnessInformation() {
+    private Program program;
+    private BitSet synthesizedVariables;
+    private PhiUpdater phiUpdater;
+    private BitSet notNullVariables;
+    private BitSet nullVariables;
+
+    NullnessInformation(Program program, BitSet synthesizedVariables, PhiUpdater phiUpdater, BitSet notNullVariables,
+            BitSet nullVariables) {
+        this.program = program;
+        this.synthesizedVariables = synthesizedVariables;
+        this.phiUpdater = phiUpdater;
+        this.notNullVariables = notNullVariables;
+        this.nullVariables = nullVariables;
+    }
+
+    public boolean isNotNull(Variable variable) {
+        return notNullVariables.get(variable.getIndex());
+    }
+
+    public boolean isNull(Variable variable) {
+        return nullVariables.get(variable.getIndex());
     }
 
     public void dispose() {
+        Set<Phi> phisToRemove = new HashSet<>(phiUpdater.getSynthesizedPhis());
+        Set<TryCatchJoint> jointsToRemove = new HashSet<>(phiUpdater.getSynthesizedJoints());
+        DefinitionExtractor defExtractor = new DefinitionExtractor();
+        InstructionVariableMapper variableMapper = new InstructionVariableMapper(var -> {
+            int source = phiUpdater.getSourceVariable(var.getIndex());
+            return source >= 0 ? program.variableAt(source) : var;
+        });
+        for (BasicBlock block : program.getBasicBlocks()) {
+            block.getPhis().removeIf(phisToRemove::contains);
+            for (TryCatchBlock tryCatch : block.getTryCatchBlocks()) {
+                tryCatch.getJoints().removeIf(jointsToRemove::contains);
+            }
+            for (Instruction insn : block) {
+                insn.acceptVisitor(defExtractor);
+                if (Arrays.stream(defExtractor.getDefinedVariables())
+                        .anyMatch(var -> synthesizedVariables.get(var.getIndex()))) {
+                    insn.delete();
+                } else {
+                    insn.acceptVisitor(variableMapper);
+                }
+            }
+        }
     }
 
-    public static NullnessInformation build(Program program) {
-        NullnessInformation instance = new NullnessInformation();
-        return instance;
+    public static NullnessInformation build(Program program, MethodDescriptor methodDescriptor) {
+        NullnessInformationBuilder builder = new NullnessInformationBuilder(program, methodDescriptor);
+        builder.build();
+        return new NullnessInformation(program, builder.synthesizedVariables, builder.phiUpdater,
+                builder.notNullVariables, builder.nullVariables);
     }
 }

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

@@ -15,11 +15,18 @@
  */
 package org.teavm.model.analysis;
 
+import com.carrotsearch.hppc.IntArrayDeque;
+import com.carrotsearch.hppc.IntDeque;
+import com.carrotsearch.hppc.IntIntMap;
+import com.carrotsearch.hppc.IntIntOpenHashMap;
+import com.carrotsearch.hppc.IntOpenHashSet;
+import com.carrotsearch.hppc.IntSet;
 import java.util.ArrayList;
 import java.util.BitSet;
 import java.util.List;
 import org.teavm.common.Graph;
 import org.teavm.common.GraphBuilder;
+import org.teavm.common.GraphUtils;
 import org.teavm.model.BasicBlock;
 import org.teavm.model.Incoming;
 import org.teavm.model.Instruction;
@@ -32,7 +39,7 @@ import org.teavm.model.Variable;
 import org.teavm.model.instructions.AbstractInstructionVisitor;
 import org.teavm.model.instructions.ArrayLengthInstruction;
 import org.teavm.model.instructions.AssignInstruction;
-import org.teavm.model.instructions.BranchingCondition;
+import org.teavm.model.instructions.BinaryBranchingInstruction;
 import org.teavm.model.instructions.BranchingInstruction;
 import org.teavm.model.instructions.ClassConstantInstruction;
 import org.teavm.model.instructions.CloneArrayInstruction;
@@ -40,7 +47,6 @@ import org.teavm.model.instructions.ConstructArrayInstruction;
 import org.teavm.model.instructions.ConstructInstruction;
 import org.teavm.model.instructions.ConstructMultiArrayInstruction;
 import org.teavm.model.instructions.GetFieldInstruction;
-import org.teavm.model.instructions.InstructionVisitor;
 import org.teavm.model.instructions.InvokeInstruction;
 import org.teavm.model.instructions.MonitorEnterInstruction;
 import org.teavm.model.instructions.MonitorExitInstruction;
@@ -49,20 +55,22 @@ import org.teavm.model.instructions.NullConstantInstruction;
 import org.teavm.model.instructions.PutFieldInstruction;
 import org.teavm.model.instructions.StringConstantInstruction;
 import org.teavm.model.instructions.UnwrapArrayInstruction;
+import org.teavm.model.util.DominatorWalker;
+import org.teavm.model.util.DominatorWalkerCallback;
 import org.teavm.model.util.PhiUpdater;
 
 class NullnessInformationBuilder {
     private Program program;
     private MethodDescriptor methodDescriptor;
-    private BitSet notNullVariables = new BitSet();
-    private BitSet nullVariables = new BitSet();
-    private BitSet synthesizedVariables = new BitSet();
-    private PhiUpdater phiUpdater;
+    BitSet notNullVariables = new BitSet();
+    BitSet nullVariables = new BitSet();
+    BitSet synthesizedVariables = new BitSet();
+    PhiUpdater phiUpdater;
     private List<NullConstantInstruction> nullInstructions = new ArrayList<>();
     private List<NullCheckInstruction> notNullInstructions = new ArrayList<>();
     private Graph assignmentGraph;
-    private int[] nullPredecessorsLeft;
     private int[] notNullPredecessorsLeft;
+    private int[] sccIndexes;
 
     NullnessInformationBuilder(Program program, MethodDescriptor methodDescriptor) {
         this.program = program;
@@ -72,12 +80,13 @@ class NullnessInformationBuilder {
     void build() {
         extendProgram();
         buildAssignmentGraph();
-        findKnownNullness();
+        propagateNullness();
     }
 
     private void extendProgram() {
         insertAdditionalVariables();
 
+        notNullVariables.set(0);
         Variable[] parameters = new Variable[methodDescriptor.parameterCount() + 1];
         for (int i = 0; i < parameters.length; ++i) {
             parameters[i] = program.variableAt(i);
@@ -89,55 +98,28 @@ class NullnessInformationBuilder {
     }
 
     private void insertAdditionalVariables() {
+        DominatorWalker walker = new DominatorWalker(program);
         NullExtensionVisitor ev = new NullExtensionVisitor();
-        for (BasicBlock block : program.getBasicBlocks()) {
-            Instruction lastInstruction = block.getLastInstruction();
-            if (lastInstruction instanceof BranchingInstruction) {
-                BranchingInstruction branching = (BranchingInstruction) lastInstruction;
-                if (branching.getCondition() == BranchingCondition.NULL) {
-                    insertNullAndNotNull(branching.getOperand(), branching.getConsequent(), branching.getAlternative());
-                } else if (branching.getCondition() == BranchingCondition.NOT_NULL) {
-                    insertNullAndNotNull(branching.getOperand(), branching.getAlternative(), branching.getConsequent());
-                }
-            }
-
-            for (Instruction instruction = block.getFirstInstruction(); instruction != null;) {
-                Instruction next = instruction.getNext();
-                instruction.acceptVisitor(ev);
-                instruction = next;
-            }
-        }
+        walker.walk(ev);
     }
 
     private void collectAdditionalVariables() {
         for (NullConstantInstruction nullInstruction : nullInstructions) {
             nullVariables.set(nullInstruction.getReceiver().getIndex());
+            synthesizedVariables.set(nullInstruction.getReceiver().getIndex());
         }
         for (NullCheckInstruction notNullInstruction : notNullInstructions) {
             notNullVariables.set(notNullInstruction.getReceiver().getIndex());
+            synthesizedVariables.set(notNullInstruction.getReceiver().getIndex());
         }
-        synthesizedVariables.or(nullVariables);
-        synthesizedVariables.or(notNullVariables);
 
         nullInstructions.clear();
         notNullInstructions.clear();
     }
 
-    private void insertNullAndNotNull(Variable variable, BasicBlock nullBlock, BasicBlock notNullBlock) {
-        NullCheckInstruction notNullInstruction = new NullCheckInstruction();
-        notNullInstruction.setValue(variable);
-        notNullInstruction.setReceiver(variable);
-        notNullBlock.addFirst(notNullInstruction);
-        notNullInstructions.add(notNullInstruction);
-
-        NullConstantInstruction nullInstruction = new NullConstantInstruction();
-        nullInstruction.setReceiver(variable);
-        nullBlock.addFirst(nullInstruction);
-        nullInstructions.add(nullInstruction);
-    }
-
     private void buildAssignmentGraph() {
-        GraphBuilder builder = new GraphBuilder();
+        GraphBuilder builder = new GraphBuilder(program.variableCount());
+
         for (BasicBlock block : program.getBasicBlocks()) {
             for (Phi phi : block.getPhis()) {
                 for (Incoming incoming : phi.getIncomings()) {
@@ -161,25 +143,93 @@ class NullnessInformationBuilder {
         }
         assignmentGraph = builder.build();
 
-        // TODO: handle SCCs
+        sccIndexes = new int[program.variableCount()];
+        if (assignmentGraph.size() > 0) {
+            int[][] sccs = GraphUtils.findStronglyConnectedComponents(assignmentGraph, new int[]{0});
+            for (int i = 0; i < sccs.length; ++i) {
+                for (int sccNode : sccs[i]) {
+                    sccIndexes[sccNode] = i + 1;
+                }
+            }
+        }
 
-        nullPredecessorsLeft = new int[assignmentGraph.size()];
         notNullPredecessorsLeft = new int[assignmentGraph.size()];
         for (int i = 0; i < assignmentGraph.size(); ++i) {
-            nullPredecessorsLeft[i] = assignmentGraph.incomingEdgesCount(i);
             notNullPredecessorsLeft[i] = assignmentGraph.incomingEdgesCount(i);
-        }
-    }
-
-    private void findKnownNullness() {
-        for (BasicBlock block : program.getBasicBlocks()) {
-            for (Instruction instruction : block) {
-                instruction.acceptVisitor(nullnessVisitor);
+            if (sccIndexes[i] > 0) {
+                for (int predecessor : assignmentGraph.outgoingEdges(i)) {
+                    if (sccIndexes[predecessor] == sccIndexes[i]) {
+                        notNullPredecessorsLeft[i]--;
+                    }
+                }
             }
         }
     }
 
-    class NullExtensionVisitor extends AbstractInstructionVisitor {
+    private void propagateNullness() {
+        if (assignmentGraph.size() == 0) {
+            return;
+        }
+
+        IntDeque deque = new IntArrayDeque();
+        for (int i = notNullVariables.nextSetBit(0); i >= 0; i = notNullVariables.nextSetBit(i + 1)) {
+            deque.addLast(i);
+        }
+        boolean[] visited = new boolean[program.variableCount()];
+
+        while (!deque.isEmpty()) {
+            int node = deque.removeFirst();
+            if (visited[node]) {
+                continue;
+            }
+            visited[node] = true;
+            for (int successor : assignmentGraph.outgoingEdges(node)) {
+                if (sccIndexes[successor] == 0 || sccIndexes[successor] != sccIndexes[node]) {
+                    if (--notNullPredecessorsLeft[successor] == 0) {
+                        deque.addLast(successor);
+                    }
+                }
+            }
+        }
+    }
+
+    class NullExtensionVisitor extends AbstractInstructionVisitor implements DominatorWalkerCallback<State> {
+        State currentState;
+        BasicBlock currentBlock;
+        IntIntMap nullSuccessors = new IntIntOpenHashMap();
+        IntIntMap notNullSuccessors = new IntIntOpenHashMap();
+
+        @Override
+        public State visit(BasicBlock block) {
+            currentState = new State();
+
+            currentBlock = block;
+            if (nullSuccessors.containsKey(block.getIndex())) {
+                int varIndex = nullSuccessors.remove(block.getIndex());
+                insertNullInstruction(program.variableAt(varIndex));
+            }
+            if (notNullSuccessors.containsKey(block.getIndex())) {
+                int varIndex = notNullSuccessors.remove(block.getIndex());
+                insertNotNullInstruction(null, program.variableAt(varIndex));
+            }
+
+            for (Instruction insn : block) {
+                insn.acceptVisitor(this);
+            }
+
+            return currentState;
+        }
+
+        @Override
+        public void endVisit(BasicBlock block, State state) {
+            for (int rollbackToNull : state.newlyNonNull.toArray()) {
+                notNullVariables.clear(rollbackToNull);
+            }
+            for (int rollbackToNotNull : state.newlyNull.toArray()) {
+                nullVariables.clear(rollbackToNotNull);
+            }
+        }
+
         @Override
         public void visit(GetFieldInstruction insn) {
             if (insn.getInstance() != null) {
@@ -226,16 +276,11 @@ class NullnessInformationBuilder {
             insertNotNullInstruction(insn, insn.getObjectRef());
         }
 
-        private void insertNotNullInstruction(Instruction currentInstruction, Variable var) {
-            NullCheckInstruction insn = new NullCheckInstruction();
-            insn.setReceiver(var);
-            insn.setValue(var);
-            notNullInstructions.add(insn);
-            currentInstruction.insertNext(insn);
+        @Override
+        public void visit(StringConstantInstruction insn) {
+            notNullVariables.set(insn.getReceiver().getIndex());
         }
-    }
 
-    private InstructionVisitor nullnessVisitor = new AbstractInstructionVisitor() {
         @Override
         public void visit(ClassConstantInstruction insn) {
             notNullVariables.set(insn.getReceiver().getIndex());
@@ -247,8 +292,9 @@ class NullnessInformationBuilder {
         }
 
         @Override
-        public void visit(StringConstantInstruction insn) {
-            notNullVariables.set(insn.getReceiver().getIndex());
+        public void visit(AssignInstruction insn) {
+            notNullVariables.set(insn.getReceiver().getIndex(), notNullVariables.get(insn.getAssignee().getIndex()));
+            nullVariables.set(insn.getReceiver().getIndex(), nullVariables.get(insn.getAssignee().getIndex()));
         }
 
         @Override
@@ -268,7 +314,95 @@ class NullnessInformationBuilder {
 
         @Override
         public void visit(NullCheckInstruction insn) {
-            super.visit(insn);
+            notNullVariables.set(insn.getReceiver().getIndex());
         }
-    };
+
+        @Override
+        public void visit(BranchingInstruction insn) {
+            switch (insn.getCondition()) {
+                case NOT_NULL:
+                    notNullSuccessors.put(insn.getConsequent().getIndex(), insn.getOperand().getIndex());
+                    nullSuccessors.put(insn.getAlternative().getIndex(), insn.getOperand().getIndex());
+                    break;
+                case NULL:
+                    nullSuccessors.put(insn.getConsequent().getIndex(), insn.getOperand().getIndex());
+                    notNullSuccessors.put(insn.getAlternative().getIndex(), insn.getOperand().getIndex());
+                    break;
+                default:
+                    break;
+            }
+        }
+
+        @Override
+        public void visit(BinaryBranchingInstruction insn) {
+            Variable first = insn.getFirstOperand();
+            Variable second = insn.getSecondOperand();
+            if (nullVariables.get(first.getIndex())) {
+                first = second;
+            } else if (!nullVariables.get(second.getIndex())) {
+                return;
+            }
+
+            switch (insn.getCondition()) {
+                case REFERENCE_EQUAL:
+                    notNullSuccessors.put(insn.getConsequent().getIndex(), first.getIndex());
+                    nullSuccessors.put(insn.getAlternative().getIndex(), first.getIndex());
+                    break;
+                case REFERENCE_NOT_EQUAL:
+                    nullSuccessors.put(insn.getConsequent().getIndex(), first.getIndex());
+                    notNullSuccessors.put(insn.getAlternative().getIndex(), first.getIndex());
+                    break;
+                default:
+                    break;
+            }
+        }
+
+        private void insertNotNullInstruction(Instruction currentInstruction, Variable var) {
+            if (notNullVariables.get(var.getIndex())) {
+                return;
+            }
+            NullCheckInstruction insn = new NullCheckInstruction();
+            insn.setReceiver(var);
+            insn.setValue(var);
+            notNullInstructions.add(insn);
+            if (currentInstruction != null) {
+                currentInstruction.insertNext(insn);
+            } else {
+                currentBlock.addFirst(insn);
+            }
+            markAsNonNull(var);
+        }
+
+        private void insertNullInstruction(Variable var) {
+            if (nullVariables.get(var.getIndex())) {
+                return;
+            }
+            NullConstantInstruction insn = new NullConstantInstruction();
+            insn.setReceiver(var);
+            nullInstructions.add(insn);
+            currentBlock.addFirst(insn);
+            markAsNull(var);
+        }
+
+        private void markAsNonNull(Variable var) {
+            if (notNullVariables.get(var.getIndex())) {
+                return;
+            }
+            notNullVariables.set(var.getIndex());
+            currentState.newlyNonNull.add(var.getIndex());
+        }
+
+        private void markAsNull(Variable var) {
+            if (nullVariables.get(var.getIndex())) {
+                return;
+            }
+            nullVariables.set(var.getIndex());
+            currentState.newlyNull.add(var.getIndex());
+        }
+    }
+
+    static class State {
+        IntSet newlyNonNull = new IntOpenHashSet();
+        IntSet newlyNull = new IntOpenHashSet();
+    }
 }

core/src/main/java/org/teavm/model/text/InstructionStringifier.java

@@ -16,8 +16,10 @@
 package org.teavm.model.text;
 
 import java.util.Arrays;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Locale;
+import java.util.Set;
 import java.util.stream.Collectors;
 import org.teavm.model.*;
 import org.teavm.model.instructions.*;
@@ -25,9 +27,29 @@ import org.teavm.model.instructions.*;
 class InstructionStringifier implements InstructionReader {
     private TextLocation location;
     private StringBuilder sb;
+    private String[] variableLabels;
 
-    InstructionStringifier(StringBuilder sb) {
+    InstructionStringifier(StringBuilder sb, ProgramReader program) {
         this.sb = sb;
+
+        variableLabels = new String[program.variableCount()];
+        Set<String> occupiedLabels = new HashSet<>();
+        for (int i = 0; i < program.variableCount(); ++i) {
+            VariableReader var = program.variableAt(i);
+            String suggestedName = var.getLabel() != null ? var.getLabel() : Integer.toString(i);
+            if (!occupiedLabels.add(suggestedName)) {
+                int suffix = 1;
+                String base = suggestedName + "_";
+                do {
+                    suggestedName = base + suffix++;
+                } while (!occupiedLabels.add(suggestedName));
+            }
+            variableLabels[i] = suggestedName;
+        }
+    }
+
+    public String getVariableLabel(int index) {
+        return variableLabels[index];
     }
 
     public TextLocation getLocation() {
@@ -44,40 +66,58 @@ class InstructionStringifier implements InstructionReader {
         sb.append("nop");
     }
 
+    InstructionStringifier append(String str) {
+        sb.append(str);
+        return this;
+    }
+
+    InstructionStringifier append(int value) {
+        sb.append(value);
+        return this;
+    }
+
+    InstructionStringifier append(char value) {
+        sb.append(value);
+        return this;
+    }
+
+    InstructionStringifier appendLocalVar(VariableReader var) {
+        return append("@").append(variableLabels[var.getIndex()]);
+    }
+
     @Override
     public void classConstant(VariableReader receiver, ValueType cst) {
-        sb.append("@").append(receiver.getIndex()).append(" := classOf ");
-        escapeIdentifierIfNeeded(cst.toString(), sb);
+        appendLocalVar(receiver).append(" := classOf ").escapeIdentifierIfNeeded(cst.toString());
     }
 
     @Override
     public void nullConstant(VariableReader receiver) {
-        sb.append("@").append(receiver.getIndex()).append(" := null");
+        appendLocalVar(receiver).append(" := null");
     }
 
     @Override
     public void integerConstant(VariableReader receiver, int cst) {
-        sb.append("@").append(receiver.getIndex()).append(" := ").append(cst);
+        appendLocalVar(receiver).append(" := " + cst);
     }
 
     @Override
     public void longConstant(VariableReader receiver, long cst) {
-        sb.append("@").append(receiver.getIndex()).append(" := ").append(cst).append("L");
+        appendLocalVar(receiver).append(" := " + cst + "L");
     }
 
     @Override
     public void floatConstant(VariableReader receiver, float cst) {
-        sb.append("@").append(receiver.getIndex()).append(" := ").append(cst).append('F');
+        appendLocalVar(receiver).append(" := " + cst + 'F');
     }
 
     @Override
     public void doubleConstant(VariableReader receiver, double cst) {
-        sb.append("@").append(receiver.getIndex()).append(" := ").append(cst);
+        appendLocalVar(receiver).append(" := " + cst);
     }
 
     @Override
     public void stringConstant(VariableReader receiver, String cst) {
-        sb.append("@").append(receiver.getIndex()).append(" := '");
+        appendLocalVar(receiver).append(" := '");
         escapeStringLiteral(cst, sb);
         sb.append("'");
     }
@@ -114,7 +154,7 @@ class InstructionStringifier implements InstructionReader {
         }
     }
 
-    private static void escapeIdentifierIfNeeded(String s, StringBuilder sb) {
+    private InstructionStringifier escapeIdentifierIfNeeded(String s) {
         boolean needsEscaping = false;
         if (s.isEmpty()) {
             needsEscaping = true;
@@ -133,87 +173,88 @@ class InstructionStringifier implements InstructionReader {
         } else {
             sb.append(s);
         }
+
+        return this;
     }
 
     @Override
     public void binary(BinaryOperation op, VariableReader receiver, VariableReader first, VariableReader second,
             NumericOperandType type) {
-        sb.append("@").append(receiver.getIndex()).append(" := @").append(first.getIndex()).append(" ");
+        appendLocalVar(receiver).append(" := ").appendLocalVar(first).append(" ");
         switch (op) {
             case ADD:
-                sb.append("+");
+                append("+");
                 break;
             case AND:
-                sb.append("&");
+                append("&");
                 break;
             case COMPARE:
-                sb.append("compareTo");
+                append("compareTo");
                 break;
             case DIVIDE:
-                sb.append("/");
+                append("/");
                 break;
             case MODULO:
-                sb.append("%");
+                append("%");
                 break;
             case MULTIPLY:
-                sb.append("*");
+                append("*");
                 break;
             case OR:
-                sb.append("|");
+                append("|");
                 break;
             case SHIFT_LEFT:
-                sb.append("<<");
+                append("<<");
                 break;
             case SHIFT_RIGHT:
-                sb.append(">>");
+                append(">>");
                 break;
             case SHIFT_RIGHT_UNSIGNED:
-                sb.append(">>>");
+                append(">>>");
                 break;
             case SUBTRACT:
-                sb.append("-");
+                append("-");
                 break;
             case XOR:
-                sb.append("^");
+                append("^");
                 break;
         }
-        sb.append(" @").append(second.getIndex());
+        append(" ").appendLocalVar(second);
     }
 
     @Override
     public void negate(VariableReader receiver, VariableReader operand, NumericOperandType type) {
-        sb.append("@").append(receiver.getIndex()).append(" := -").append(" @").append(operand.getIndex());
+        appendLocalVar(receiver).append(" := -").append(" ").appendLocalVar(operand);
     }
 
     @Override
     public void assign(VariableReader receiver, VariableReader assignee) {
-        sb.append("@").append(receiver.getIndex()).append(" := @").append(assignee.getIndex());
+        appendLocalVar(receiver).append(" := ").appendLocalVar(assignee);
     }
 
     @Override
     public void cast(VariableReader receiver, VariableReader value, ValueType targetType) {
-        sb.append("@").append(receiver.getIndex()).append(" := cast @").append(value.getIndex())
-                .append(" to ");
-        escapeIdentifierIfNeeded(targetType.toString(), sb);
+        appendLocalVar(receiver).append(" := cast ").appendLocalVar(value).append(" to ")
+                .escapeIdentifierIfNeeded(targetType.toString());
     }
 
     @Override
     public void cast(VariableReader receiver, VariableReader value, NumericOperandType sourceType,
             NumericOperandType targetType) {
-        sb.append("@").append(receiver.getIndex()).append(" := cast @").append(value.getIndex())
-                .append(" from ").append(sourceType).append(" to ").append(targetType);
+        appendLocalVar(receiver).append(" := cast ").appendLocalVar(value)
+                .append(" from ").append(sourceType.toString()).append(" to ").append(targetType.toString());
     }
 
     @Override
     public void cast(VariableReader receiver, VariableReader value, IntegerSubtype type,
             CastIntegerDirection direction) {
-        sb.append("@").append(receiver.getIndex()).append(" := cast @").append(value.getIndex());
+        appendLocalVar(receiver).append(" := cast ").appendLocalVar(value);
         switch (direction) {
             case FROM_INTEGER:
-                sb.append(" from int to ").append(type.name().toLowerCase(Locale.ROOT));
+                append(" from int to ").append(type.name().toLowerCase(Locale.ROOT));
                 break;
             case TO_INTEGER:
-                sb.append(" from ").append(type.name().toLowerCase(Locale.ROOT)).append(" to int");
+                append(" from ").append(type.name().toLowerCase(Locale.ROOT)).append(" to int");
                 break;
         }
     }
@@ -221,7 +262,7 @@ class InstructionStringifier implements InstructionReader {
     @Override
     public void jumpIf(BranchingCondition cond, VariableReader operand, BasicBlockReader consequent,
             BasicBlockReader alternative) {
-        sb.append("if @").append(operand.getIndex()).append(" ");
+        append("if ").appendLocalVar(operand).append(" ");
         switch (cond) {
             case EQUAL:
                 sb.append("== 0");
@@ -248,174 +289,164 @@ class InstructionStringifier implements InstructionReader {
                 sb.append("=== null");
                 break;
         }
-        sb.append(" then goto $").append(consequent.getIndex()).append(" else goto $").append(alternative.getIndex());
+        append(" then goto $").append(consequent.getIndex()).append(" else goto $").append(alternative.getIndex());
     }
 
     @Override
     public void jumpIf(BinaryBranchingCondition cond, VariableReader first, VariableReader second,
             BasicBlockReader consequent, BasicBlockReader alternative) {
-        sb.append("if @").append(first.getIndex()).append(" ");
+        append("if ").appendLocalVar(first).append(" ");
         switch (cond) {
             case EQUAL:
-                sb.append("==");
+                append("==");
                 break;
             case REFERENCE_EQUAL:
-                sb.append("===");
+                append("===");
                 break;
             case NOT_EQUAL:
-                sb.append("!=");
+                append("!=");
                 break;
             case REFERENCE_NOT_EQUAL:
-                sb.append("!==");
+                append("!==");
                 break;
         }
-        sb.append("@").append(second.getIndex()).append(" then goto $").append(consequent.getIndex())
+        appendLocalVar(second).append(" then goto $").append(consequent.getIndex())
                 .append(" else goto $").append(alternative.getIndex());
     }
 
     @Override
     public void jump(BasicBlockReader target) {
-        sb.append("goto $").append(target.getIndex());
+        append("goto $").append(target.getIndex());
     }
 
     @Override
     public void choose(VariableReader condition, List<? extends SwitchTableEntryReader> table,
             BasicBlockReader defaultTarget) {
-        sb.append("switch @").append(condition.getIndex()).append(" ");
+        append("switch ").appendLocalVar(condition).append(" ");
         for (int i = 0; i < table.size(); ++i) {
             if (i > 0) {
-                sb.append(" ");
+                append(" ");
             }
             SwitchTableEntryReader entry = table.get(i);
-            sb.append("case ").append(entry.getCondition()).append(" goto $").append(entry.getTarget().getIndex());
+            append("case ").append(entry.getCondition()).append(" goto $").append(entry.getTarget().getIndex());
         }
         sb.append(" else goto $").append(defaultTarget.getIndex());
     }
 
     @Override
     public void exit(VariableReader valueToReturn) {
-        sb.append("return");
+        append("return");
         if (valueToReturn != null) {
-            sb.append(" @").append(valueToReturn.getIndex());
+            append(" ").appendLocalVar(valueToReturn);
         }
     }
 
     @Override
     public void raise(VariableReader exception) {
-        sb.append("throw @").append(exception.getIndex());
+        append("throw ").appendLocalVar(exception);
     }
 
     @Override
     public void createArray(VariableReader receiver, ValueType itemType, VariableReader size) {
-        sb.append("@").append(receiver.getIndex()).append(" := new ");
-        escapeIdentifierIfNeeded(itemType.toString(), sb);
-        sb.append("[@").append(size.getIndex()).append(']');
+        appendLocalVar(receiver).append(" := new ").escapeIdentifierIfNeeded(itemType.toString())
+                .append("[").appendLocalVar(size).append(']');
     }
 
     @Override
     public void createArray(VariableReader receiver, ValueType itemType, List<? extends VariableReader> dimensions) {
-        sb.append("@").append(receiver.getIndex()).append(" := newArray ");
-        escapeIdentifierIfNeeded(itemType.toString(), sb);
-        sb.append("[");
+        appendLocalVar(receiver).append(" := newArray ").escapeIdentifierIfNeeded(itemType.toString());
+        append("[");
 
         for (int i = 0; i < dimensions.size(); ++i) {
             if (i > 0) {
-                sb.append(", ");
+                append(", ");
             }
-            sb.append("@").append(dimensions.get(i).getIndex());
+            appendLocalVar(dimensions.get(i));
         }
-        sb.append("]");
+        append("]");
     }
 
     @Override
     public void create(VariableReader receiver, String type) {
-        sb.append("@").append(receiver.getIndex()).append(" := newArray ");
-        escapeIdentifierIfNeeded(type, sb);
+        appendLocalVar(receiver).append(" := newArray ").escapeIdentifierIfNeeded(type);
     }
 
     @Override
     public void getField(VariableReader receiver, VariableReader instance, FieldReference field, ValueType fieldType) {
-        sb.append("@").append(receiver.getIndex()).append(" := field ");
-        escapeIdentifierIfNeeded(field.toString(), sb);
+        appendLocalVar(receiver).append(" := field ").escapeIdentifierIfNeeded(field.toString());
         if (instance != null) {
-            sb.append(" @").append(instance.getIndex());
+            append(" ").appendLocalVar(instance);
         }
-        sb.append(" as ");
-        escapeIdentifierIfNeeded(fieldType.toString(), sb);
+        append(" as ").escapeIdentifierIfNeeded(fieldType.toString());
     }
 
     @Override
     public void putField(VariableReader instance, FieldReference field, VariableReader value, ValueType fieldType) {
-        sb.append("field ");
-        escapeIdentifierIfNeeded(field.toString(), sb);
+        append("field ").escapeIdentifierIfNeeded(field.toString());
         if (instance != null) {
-            sb.append(" @").append(instance.getIndex());
+            append(" ").appendLocalVar(instance);
         }
-        sb.append(" := @").append(value.getIndex());
-        sb.append(" as ");
-        escapeIdentifierIfNeeded(fieldType.toString(), sb);
+        append(" := ").appendLocalVar(value).append(" as ").escapeIdentifierIfNeeded(fieldType.toString());
     }
 
     @Override
     public void arrayLength(VariableReader receiver, VariableReader array) {
-        sb.append("@").append(receiver.getIndex()).append(" := lengthOf @").append(array.getIndex());
+        appendLocalVar(receiver).append(" := lengthOf ").appendLocalVar(array);
     }
 
     @Override
     public void cloneArray(VariableReader receiver, VariableReader array) {
-        sb.append("@").append(receiver.getIndex()).append(" := clone @").append(array.getIndex());
+        appendLocalVar(receiver).append(" := clone ").appendLocalVar(array);
     }
 
     @Override
     public void unwrapArray(VariableReader receiver, VariableReader array, ArrayElementType elementType) {
-        sb.append("@").append(receiver.getIndex()).append(" := data @").append(array.getIndex()).append(" as ")
+        appendLocalVar(receiver).append(" := data ").appendLocalVar(array).append(" as ")
                 .append(elementType.name().toLowerCase(Locale.ROOT));
     }
 
     @Override
     public void getElement(VariableReader receiver, VariableReader array, VariableReader index,
             ArrayElementType type) {
-        sb.append("@").append(receiver.getIndex()).append(" := @").append(array.getIndex()).append("[@")
-                .append(index.getIndex()).append("]").append(" as " + type.name().toLowerCase(Locale.ROOT));
+        appendLocalVar(receiver).append(" := ").appendLocalVar(array).append("[").appendLocalVar(index).append("]")
+                .append(" as " + type.name().toLowerCase(Locale.ROOT));
     }
 
     @Override
     public void putElement(VariableReader array, VariableReader index, VariableReader value, ArrayElementType type) {
-        sb.append("@").append(array.getIndex()).append("[@").append(index.getIndex()).append("] := @")
-                .append(value.getIndex()).append(" as " + type.name().toLowerCase());
+        appendLocalVar(array).append("[").appendLocalVar(index).append("] := ").appendLocalVar(value)
+                .append(" as " + type.name().toLowerCase(Locale.ROOT));
     }
 
     @Override
     public void invoke(VariableReader receiver, VariableReader instance, MethodReference method,
             List<? extends VariableReader> arguments, InvocationType type) {
         if (receiver != null) {
-            sb.append("@").append(receiver.getIndex()).append(" := ");
+            appendLocalVar(receiver).append(" := ");
         }
         if (instance == null) {
-            sb.append("invokeStatic ");
+            append("invokeStatic ");
         } else {
             switch (type) {
                 case SPECIAL:
-                    sb.append("invoke ");
+                    append("invoke ");
                     break;
                 case VIRTUAL:
-                    sb.append("invokeVirtual ");
+                    append("invokeVirtual ");
                     break;
             }
         }
 
-        escapeIdentifierIfNeeded(method.toString(), sb);
+        escapeIdentifierIfNeeded(method.toString());
         if (instance != null) {
-            sb.append(' ');
-            sb.append("@").append(instance.getIndex());
+            append(' ').appendLocalVar(instance);
         }
 
         for (int i = 0; i < arguments.size(); ++i) {
             if (instance != null || i > 0) {
-                sb.append(",");
+                append(",");
             }
-            sb.append(' ');
-            sb.append("@").append(arguments.get(i).getIndex());
+            append(' ').appendLocalVar(arguments.get(i));
         }
     }
 
@@ -424,17 +455,17 @@ class InstructionStringifier implements InstructionReader {
             List<? extends VariableReader> arguments, MethodHandle bootstrapMethod,
             List<RuntimeConstant> bootstrapArguments) {
         if (receiver != null) {
-            sb.append("@").append(receiver.getIndex()).append(" := ");
+            appendLocalVar(receiver).append(" := ");
         }
         if (instance != null) {
-            sb.append("@").append(instance.getIndex()).append(".");
+            appendLocalVar(instance).append(".");
         }
-        sb.append(method.getName()).append("(");
-        sb.append(arguments.stream().map(arg -> "@"  + arg.getIndex()).collect(Collectors.joining(", ")));
-        sb.append(") ");
-        sb.append("[").append(convert(bootstrapMethod)).append('(');
-        sb.append(bootstrapArguments.stream().map(this::convert).collect(Collectors.joining(", ")));
-        sb.append(")");
+        append(method.getName()).append("(");
+        append(arguments.stream().map(arg -> "@" + arg.getIndex()).collect(Collectors.joining(", ")));
+        append(") ");
+        append("[").append(convert(bootstrapMethod)).append('(');
+        append(bootstrapArguments.stream().map(this::convert).collect(Collectors.joining(", ")));
+        append(")");
     }
 
     private String convert(MethodHandle handle) {
@@ -488,28 +519,27 @@ class InstructionStringifier implements InstructionReader {
 
     @Override
     public void isInstance(VariableReader receiver, VariableReader value, ValueType type) {
-        sb.append("@").append(receiver.getIndex()).append(" := @").append(value.getIndex())
-                .append(" instanceOf ");
-        escapeIdentifierIfNeeded(type.toString(), sb);
+        appendLocalVar(receiver).append(" := ").appendLocalVar(value).append(" instanceOf ")
+                .escapeIdentifierIfNeeded(type.toString());
     }
 
     @Override
     public void initClass(String className) {
-        sb.append("initClass ").append(className);
+        append("initClass ").append(className);
     }
 
     @Override
     public void nullCheck(VariableReader receiver, VariableReader value) {
-        sb.append("@").append(receiver.getIndex()).append(" := nullCheck @").append(value.getIndex());
+        appendLocalVar(receiver).append(" := nullCheck ").appendLocalVar(value);
     }
 
     @Override
     public void monitorEnter(VariableReader objectRef) {
-        sb.append("monitorEnter @").append(objectRef.getIndex());
+        append("monitorEnter ").appendLocalVar(objectRef);
     }
 
     @Override
     public void monitorExit(VariableReader objectRef) {
-        sb.append("monitorExit @").append(objectRef.getIndex());
+        append("monitorExit ").appendLocalVar(objectRef);
     }
 }

core/src/main/java/org/teavm/model/text/ListingBuilder.java

@@ -24,13 +24,13 @@ public class ListingBuilder {
     public String buildListing(ProgramReader program, String prefix) {
         StringBuilder sb = new StringBuilder();
         StringBuilder insnSb = new StringBuilder();
-        InstructionStringifier stringifier = new InstructionStringifier(insnSb);
+        InstructionStringifier stringifier = new InstructionStringifier(insnSb, program);
         for (int i = 0; i < program.variableCount(); ++i) {
             VariableReader var = program.variableAt(i);
             if (var == null || var.getDebugName() == null) {
                 continue;
             }
-            sb.append(prefix).append("var @").append(i);
+            sb.append(prefix).append("var @").append(stringifier.getVariableLabel(i));
             sb.append('\n');
         }
         for (int i = 0; i < program.basicBlockCount(); ++i) {
@@ -41,20 +41,21 @@ public class ListingBuilder {
             }
 
             if (block.getExceptionVariable() != null) {
-                sb.append("    @").append(block.getExceptionVariable().getIndex()).append(" = exception\n");
+                sb.append("    ").append(stringifier.getVariableLabel(block.getExceptionVariable().getIndex()))
+                        .append(" = exception\n");
             }
 
             for (PhiReader phi : block.readPhis()) {
                 sb.append(prefix).append("    ");
-                sb.append("@").append(phi.getReceiver().getIndex()).append(" := phi ");
+                sb.append("@").append(stringifier.getVariableLabel(phi.getReceiver().getIndex())).append(" := phi ");
                 List<? extends IncomingReader> incomings = phi.readIncomings();
                 for (int j = 0; j < incomings.size(); ++j) {
                     if (j > 0) {
                         sb.append(", ");
                     }
                     IncomingReader incoming = incomings.get(j);
-                    sb.append("@").append(incoming.getValue().getIndex()).append(" from ")
-                            .append("$").append(incoming.getSource().getIndex());
+                    sb.append("@").append(stringifier.getVariableLabel(incoming.getValue().getIndex()))
+                            .append(" from ").append("$").append(incoming.getSource().getIndex());
                 }
                 sb.append("\n");
             }
@@ -86,8 +87,10 @@ public class ListingBuilder {
                 sb.append(" goto $").append(tryCatch.getHandler().getIndex());
                 sb.append("\n");
                 for (TryCatchJointReader joint : tryCatch.readJoints()) {
-                    sb.append("      @").append(joint.getReceiver().getIndex()).append(" := ephi ");
-                    sb.append(joint.readSourceVariables().stream().map(sourceVar -> "@" + sourceVar.getIndex())
+                    sb.append("      @").append(stringifier.getVariableLabel(joint.getReceiver().getIndex()))
+                            .append(" := ephi ");
+                    sb.append(joint.readSourceVariables().stream()
+                            .map(sourceVar -> "@" + stringifier.getVariableLabel(sourceVar.getIndex()))
                             .collect(Collectors.joining(", ")));
                     sb.append("\n");
                 }

core/src/main/java/org/teavm/model/text/ListingParser.java

@@ -72,6 +72,7 @@ import org.teavm.model.instructions.MonitorEnterInstruction;
 import org.teavm.model.instructions.MonitorExitInstruction;
 import org.teavm.model.instructions.NegateInstruction;
 import org.teavm.model.instructions.NullCheckInstruction;
+import org.teavm.model.instructions.NullConstantInstruction;
 import org.teavm.model.instructions.NumericOperandType;
 import org.teavm.model.instructions.PutElementInstruction;
 import org.teavm.model.instructions.PutFieldInstruction;
@@ -349,6 +350,13 @@ public class ListingParser {
             case IDENTIFIER: {
                 String keyword = (String) lexer.getTokenValue();
                 switch (keyword) {
+                    case "null": {
+                        lexer.nextToken();
+                        NullConstantInstruction insn = new NullConstantInstruction();
+                        insn.setReceiver(receiver);
+                        addInstruction(insn);
+                        break;
+                    }
                     case "phi":
                         lexer.nextToken();
                         parsePhi(receiver);

core/src/main/java/org/teavm/model/util/DominatorWalker.java

@@ -0,0 +1,63 @@
+/*
+ *  Copyright 2016 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.model.util;
+
+import org.teavm.common.DominatorTree;
+import org.teavm.common.Graph;
+import org.teavm.common.GraphUtils;
+import org.teavm.model.BasicBlock;
+import org.teavm.model.Program;
+
+public class DominatorWalker {
+    private Program program;
+    private Graph domGraph;
+
+    public DominatorWalker(Program program) {
+        this.program = program;
+        Graph cfg = ProgramUtils.buildControlFlowGraph(program);
+        DominatorTree dom = GraphUtils.buildDominatorTree(cfg);
+        domGraph = GraphUtils.buildDominatorGraph(dom, cfg.size());
+    }
+
+    public <T> void walk(DominatorWalkerCallback<T> callback) {
+        int[] stack = new int[program.basicBlockCount() * 2];
+        Object[] stateStack = new Object[stack.length];
+        boolean[] backward = new boolean[stack.length];
+
+        int head = 1;
+        while (head > 0) {
+            int node = stack[--head];
+            BasicBlock block = program.basicBlockAt(node);
+            if (backward[head]) {
+                @SuppressWarnings("unchecked")
+                T state = (T) stateStack[head];
+                callback.endVisit(block, state);
+            } else if (callback.filter(block)) {
+                stack[head] = node;
+                backward[head] = true;
+                stateStack[head] = callback.visit(block);
+                head++;
+
+                int[] successors = domGraph.outgoingEdges(node);
+                for (int i = successors.length - 1; i >= 0; --i) {
+                    stack[head] = successors[i];
+                    backward[head] = false;
+                    head++;
+                }
+            }
+        }
+    }
+}

core/src/main/java/org/teavm/model/util/DominatorWalkerCallback.java

@@ -0,0 +1,44 @@
+/*
+ *  Copyright 2016 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.model.util;
+
+import org.teavm.model.BasicBlock;
+
+/**
+ * An object that receives information from {@link DominatorWalker}
+ *
+ * @param <T> type of state that can be saved for each visited node.
+ */
+public interface DominatorWalkerCallback<T> {
+    /**
+     * Called before visiting block. This method should tell whether this block and all of its descendant blocks
+     * should be visited.
+     */
+    default boolean filter(BasicBlock block) {
+        return true;
+    }
+
+    /**
+     * Visits block and returns visit state. This state is saved by walker and then passed to
+     * {@link #endVisit(BasicBlock, Object)} after all of this block's descendants visited.
+     *
+     * @return state that further will be passed to {@link #endVisit(BasicBlock, Object)}
+     */
+    T visit(BasicBlock block);
+
+    default void endVisit(BasicBlock block, T state) {
+    }
+}

core/src/main/java/org/teavm/model/util/PhiUpdater.java

@@ -105,7 +105,7 @@ public class PhiUpdater {
         return variableToSourceMap.get(var);
     }
 
-    public List<Phi> getSynthesizedPhisBy() {
+    public List<Phi> getSynthesizedPhis() {
         return synthesizedPhis;
     }
 
@@ -232,6 +232,7 @@ public class PhiUpdater {
             for (Phi phi : synthesizedPhisByBlock.get(index)) {
                 Variable var = program.createVariable();
                 var.setDebugName(phi.getReceiver().getDebugName());
+                var.setLabel(phi.getReceiver().getLabel());
                 mapVariable(phi.getReceiver().getIndex(), var);
                 phisByReceiver.put(var.getIndex(), phi);
                 phi.setReceiver(var);
@@ -269,6 +270,7 @@ public class PhiUpdater {
                 for (TryCatchJoint joint : synthesizedJointsByBlock.get(index).get(i)) {
                     Variable var = program.createVariable();
                     var.setDebugName(joint.getReceiver().getDebugName());
+                    var.setLabel(joint.getReceiver().getLabel());
                     mapVariable(joint.getReceiver().getIndex(), var);
                     joint.setReceiver(var);
                     jointsByReceiver.put(var.getIndex(), joint);
@@ -277,7 +279,8 @@ public class PhiUpdater {
             variableMap = regularVariableMap;
 
             int[] successors = domGraph.outgoingEdges(index);
-            for (int successor : successors) {
+            for (int j = successors.length - 1; j >= 0; --j) {
+                int successor = successors[j];
                 Task next = new Task();
                 next.variables = (catchSuccessors.contains(successor) ? catchVariableMap : variableMap).clone();
                 next.block = program.basicBlockAt(successor);
@@ -473,7 +476,10 @@ public class PhiUpdater {
         if (!usedDefinitions[var.getIndex()]) {
             usedDefinitions[var.getIndex()] = true;
         } else {
+            Variable old = var;
             var = program.createVariable();
+            var.setDebugName(old.getDebugName());
+            var.setLabel(old.getLabel());
         }
 
         return var;

core/src/main/java/org/teavm/model/util/ProgramUtils.java

@@ -16,8 +16,10 @@
 package org.teavm.model.util;
 
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
 import java.util.Map;
+import java.util.Set;
 import org.teavm.common.Graph;
 import org.teavm.common.GraphBuilder;
 import org.teavm.model.BasicBlock;
@@ -219,4 +221,24 @@ public final class ProgramUtils {
         }
         return places;
     }
+
+    public static void makeUniqueLabels(Program program) {
+        Set<String> occupiedLabels = new HashSet<>();
+
+        for (int i = 0; i < program.variableCount(); ++i) {
+            Variable var = program.variableAt(i);
+            if (var.getLabel() == null) {
+                continue;
+            }
+            String suggestedName = var.getLabel();
+            if (!occupiedLabels.add(suggestedName)) {
+                int suffix = 1;
+                String base = suggestedName + "_";
+                do {
+                    suggestedName = base + suffix++;
+                } while (!occupiedLabels.add(suggestedName));
+            }
+            var.setLabel(suggestedName);
+        }
+    }
 }

core/src/test/java/org/teavm/model/analysis/test/NullnessAnalysisTest.java

@@ -0,0 +1,155 @@
+/*
+ *  Copyright 2016 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.model.analysis.test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotNull;
+import com.carrotsearch.hppc.IntIntMap;
+import com.carrotsearch.hppc.IntIntOpenHashMap;
+import com.carrotsearch.hppc.ObjectByteMap;
+import com.carrotsearch.hppc.ObjectByteOpenHashMap;
+import com.carrotsearch.hppc.ObjectIntMap;
+import com.carrotsearch.hppc.cursors.ObjectCursor;
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+import java.io.Reader;
+import java.util.HashMap;
+import java.util.Map;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TestName;
+import org.teavm.model.MethodDescriptor;
+import org.teavm.model.Program;
+import org.teavm.model.ValueType;
+import org.teavm.model.Variable;
+import org.teavm.model.analysis.NullnessInformation;
+import org.teavm.model.text.ListingBuilder;
+import org.teavm.model.text.ListingParseException;
+import org.teavm.model.text.ListingParser;
+import org.teavm.model.util.ProgramUtils;
+
+public class NullnessAnalysisTest {
+    @Rule
+    public TestName name = new TestName();
+
+    private static final String NOT_NULL_DIRECTIVE = "// NOT_NULL ";
+    private static final String NULLABLE_DIRECTIVE = "// NULLABLE ";
+
+    @Test
+    public void simple() {
+        test();
+    }
+
+    @Test
+    public void phiJoin() {
+        test();
+    }
+
+    @Test
+    public void branch() {
+        test();
+    }
+
+    private void test() {
+        String baseName = "model/analysis/" + name.getMethodName();
+        String originalResourceName = baseName + ".original.txt";
+        String extendedResourceName = baseName + ".extended.txt";
+        Program originalProgram = parseResource(originalResourceName);
+        Program extendedProgram = parseResource(extendedResourceName);
+
+        ListingBuilder listingBuilder = new ListingBuilder();
+        String listingBeforeExtension = listingBuilder.buildListing(originalProgram, "");
+
+        NullnessInformation information = NullnessInformation.build(originalProgram,
+                new MethodDescriptor("foo", ValueType.VOID));
+
+        ProgramUtils.makeUniqueLabels(originalProgram);
+        String actualListing = listingBuilder.buildListing(originalProgram, "");
+        String expectedListing = listingBuilder.buildListing(extendedProgram, "");
+
+        assertEquals(expectedListing, actualListing);
+
+        ObjectByteMap<String> expectedNullness = extractExpectedNullness(extendedResourceName);
+        Map<String, Variable> variablesByLabel = variablesByLabel(originalProgram);
+        for (ObjectCursor<String> varNameCursor : expectedNullness.keys()) {
+            String varName = varNameCursor.value;
+            Variable var = variablesByLabel.get(varName);
+            assertNotNull("Variable " + varName + " is missing", var);
+            boolean notNull = expectedNullness.get(varName) != 0;
+            assertEquals("Variable " + varName + " non-null", notNull, information.isNotNull(var));
+        }
+
+        information.dispose();
+        String listingAfterDispose = listingBuilder.buildListing(originalProgram, "");
+        assertEquals(listingBeforeExtension, listingAfterDispose);
+    }
+
+    private Program parseResource(String name) {
+        ClassLoader classLoader = NullnessAnalysisTest.class.getClassLoader();
+        try (InputStream input = classLoader.getResourceAsStream(name);
+                Reader reader = new InputStreamReader(input, "UTF-8")) {
+            return new ListingParser().parse(reader);
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        } catch (ListingParseException e) {
+            throw new RuntimeException("at " + e.getIndex() + "", e);
+        }
+    }
+
+    private ObjectByteMap<String> extractExpectedNullness(String name) {
+        ClassLoader classLoader = NullnessAnalysisTest.class.getClassLoader();
+        try (InputStream input = classLoader.getResourceAsStream(name);
+                BufferedReader reader = new BufferedReader(new InputStreamReader(input, "UTF-8"))) {
+            ObjectByteMap<String> result = new ObjectByteOpenHashMap<>();
+
+            while (true) {
+                String line = reader.readLine();
+                if (line == null) {
+                    break;
+                }
+
+                int index = line.indexOf(NOT_NULL_DIRECTIVE);
+                if (index >= 0) {
+                    String variable = line.substring(index + NOT_NULL_DIRECTIVE.length()).trim();
+                    result.put(variable, (byte) 1);
+                }
+
+                index = line.indexOf(NULLABLE_DIRECTIVE);
+                if (index >= 0) {
+                    String variable = line.substring(index + NULLABLE_DIRECTIVE.length()).trim();
+                    result.put(variable, (byte) 0);
+                }
+            }
+
+            return result;
+        } catch (IOException e) {
+            throw new RuntimeException(e);
+        }
+    }
+
+    private Map<String, Variable> variablesByLabel(Program program) {
+        Map<String, Variable> result = new HashMap<>();
+        for (int i = 0; i < program.variableCount(); ++i) {
+            Variable var = program.variableAt(i);
+            if (var.getLabel() != null) {
+                result.put(var.getLabel(), var);
+            }
+        }
+        return result;
+    }
+}

core/src/test/resources/model/analysis/branch.extended.txt

@@ -0,0 +1,21 @@
+var @this as this
+
+$start
+    @v := invokeStatic `Foo.get()LFoo;`
+    if @v === null then goto $ifNull else goto $ifNotNull
+$ifNull
+    @v_1 := null
+    invokeVirtual `Foo.bar()V` @v_1
+    @v_2 := nullCheck @v_1
+    goto $join
+$ifNotNull
+    @v_3 := nullCheck @v
+    invokeVirtual `Foo.baz()V` @v_3
+    goto $join
+$join
+    return
+
+// NULLABLE v
+// NULLABLE v_1
+// NOT_NULL v_2
+// NOT_NULL v_3

core/src/test/resources/model/analysis/branch.original.txt

@@ -0,0 +1,13 @@
+var @this as this
+
+$start
+    @v := invokeStatic `Foo.get()LFoo;`
+    if @v === null then goto $ifNull else goto $ifNotNull
+$ifNull
+    invokeVirtual `Foo.bar()V` @v
+    goto $join
+$ifNotNull
+    invokeVirtual `Foo.baz()V` @v
+    goto $join
+$join
+    return

core/src/test/resources/model/analysis/phiJoin.extended.txt

@@ -0,0 +1,21 @@
+$start
+    if @cond === null then goto $ifNull else goto $ifNotNull
+$ifNull
+    @cond_1 := null
+    @a := 'qwe'
+    goto $join
+$ifNotNull
+    @cond_2 := nullCheck @cond
+    @b := invokeStatic `org.test.Foo.bar()Ljava/lang/String;`
+    @b_1 := nullCheck @b
+    goto $join
+$join
+    @c := phi @a from $ifNull, @b from $ifNotNull
+    @d := phi @a from $ifNull, @b_1 from $ifNotNull
+    return @c
+
+// NULLABLE: b
+// NOT_NULL: b_1
+// NOT_NULL: a
+// NULLABLE: c
+// NOT_NULL: d

core/src/test/resources/model/analysis/phiJoin.original.txt

@@ -0,0 +1,13 @@
+$start
+    if @cond === null then goto $ifNull else goto $ifNotNull
+$ifNull
+    @a := 'qwe'
+    goto $join
+$ifNotNull
+    @b := invokeStatic `org.test.Foo.bar()Ljava/lang/String;`
+    @b_1 := nullCheck @b
+    goto $join
+$join
+    @c := phi @a from $ifNull, @b from $ifNotNull
+    @d := phi @a from $ifNull, @b_1 from $ifNotNull
+    return @c

core/src/test/resources/model/analysis/simple.extended.txt

@@ -0,0 +1,10 @@
+var @this as this
+
+$0
+    @a := invokeStatic `Foo.bar()Ljava/lang/Object;`
+    invokeVirtual `java.lang.Object.toString()Ljava/lang/String;` @a
+    @a_1 := nullCheck @a
+    return @a_1
+
+// NULLABLE a
+// NOT_NULL a_1

core/src/test/resources/model/analysis/simple.original.txt

@@ -0,0 +1,6 @@
+var @this as this
+
+$0
+    @a := invokeStatic `Foo.bar()Ljava/lang/Object;`
+    invokeVirtual `java.lang.Object.toString()Ljava/lang/String;` @a
+    return @a