Support generations in GC

classlib/src/main/java/org/teavm/classlib/java/lang/TSystem.java

@@ -121,6 +121,7 @@ public final class TSystem extends TObject {
         int itemSize = type.itemType.size;
         if ((type.itemType.flags & RuntimeClass.PRIMITIVE) == 0) {
             itemSize = Address.sizeOf();
+            GC.writeBarrier(dest);
         }
 
         Address srcAddress = Address.align(src.toAddress().add(RuntimeArray.class, 1), itemSize);
@@ -253,7 +254,7 @@ public final class TSystem extends TObject {
     }
 
     private static void gcLowLevel() {
-        GC.collectGarbage();
+        GC.collectGarbageFull();
     }
 
     public static void runFinalization() {

core/src/main/java/org/teavm/backend/c/CTarget.java

@@ -118,6 +118,7 @@ import org.teavm.model.lowlevel.ClassInitializerTransformer;
 import org.teavm.model.lowlevel.ExportDependencyListener;
 import org.teavm.model.lowlevel.LowLevelNullCheckFilter;
 import org.teavm.model.lowlevel.ShadowStackTransformer;
+import org.teavm.model.lowlevel.WriteBarrierInsertion;
 import org.teavm.model.optimization.InliningFilterFactory;
 import org.teavm.model.transformation.BoundCheckInsertion;
 import org.teavm.model.transformation.ClassPatch;
@@ -155,6 +156,7 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
     private ClassInitializerEliminator classInitializerEliminator;
     private ClassInitializerTransformer classInitializerTransformer;
     private ShadowStackTransformer shadowStackTransformer;
+    private WriteBarrierInsertion writeBarrierInsertion;
     private NullCheckInsertion nullCheckInsertion;
     private BoundCheckInsertion boundCheckInsertion = new BoundCheckInsertion();
     private CheckInstructionTransformation checkTransformation;
@@ -235,6 +237,7 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
         shadowStackTransformer = new ShadowStackTransformer(characteristics, !longjmpUsed);
         nullCheckInsertion = new NullCheckInsertion(new LowLevelNullCheckFilter(characteristics));
         checkTransformation = new CheckInstructionTransformation();
+        writeBarrierInsertion = new WriteBarrierInsertion(characteristics);
 
         controller.addVirtualMethods(VIRTUAL_METHODS::contains);
     }
@@ -272,6 +275,7 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
         dependencyAnalyzer.linkMethod(new MethodReference(GC.class, "fixHeap", void.class)).use();
         dependencyAnalyzer.linkMethod(new MethodReference(GC.class, "tryShrink", void.class)).use();
         dependencyAnalyzer.linkMethod(new MethodReference(GC.class, "collectGarbage", void.class)).use();
+        dependencyAnalyzer.linkMethod(new MethodReference(GC.class, "collectGarbageFull", void.class)).use();
 
         dependencyAnalyzer.linkMethod(new MethodReference(ExceptionHandling.class, "throwException",
                 Throwable.class, void.class)).use();
@@ -350,6 +354,7 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
                 ? this.shadowStackTransformer
                 : new ShadowStackTransformer(characteristics, !longjmpUsed);
         shadowStackTransformer.apply(program, method);
+        writeBarrierInsertion.apply(program);
     }
 
     @Override
@@ -392,6 +397,7 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
 
         stringPool = new SimpleStringPool();
         boolean vmAssertions = Boolean.parseBoolean(System.getProperty("teavm.c.vmAssertions", "false"));
+        boolean gcStats = Boolean.parseBoolean(System.getProperty("teavm.c.gcStats", "false"));
         GenerationContext context = new GenerationContext(vtableProvider, characteristics,
                 controller.getDependencyInfo(), stringPool, nameProvider, controller.getDiagnostics(), classes,
                 intrinsics, generators, asyncMethods::contains, buildTarget,
@@ -417,6 +423,9 @@ public class CTarget implements TeaVMTarget, TeaVMCHost {
         if (obfuscated) {
             configHeaderWriter.println("#define TEAVM_OBFUSCATED 1");
         }
+        if (gcStats) {
+            configHeaderWriter.println("#define TEAVM_GC_STATS 1");
+        }
 
         ClassGenerator classGenerator = new ClassGenerator(context, tagRegistry, decompiler,
                 controller.getCacheStatus());

core/src/main/java/org/teavm/backend/c/intrinsic/AllocatorIntrinsic.java

@@ -32,6 +32,7 @@ public class AllocatorIntrinsic implements Intrinsic {
 
         switch (method.getName()) {
             case "fillZero":
+            case "fill":
             case "moveMemoryBlock":
             case "isInitialized":
                 return true;
@@ -51,6 +52,16 @@ public class AllocatorIntrinsic implements Intrinsic {
                 context.emit(invocation.getArguments().get(1));
                 context.writer().print(")");
                 break;
+            case "fill":
+                context.includes().addInclude("<string.h>");
+                context.writer().print("memset(");
+                context.emit(invocation.getArguments().get(0));
+                context.writer().print(", ");
+                context.emit(invocation.getArguments().get(1));
+                context.writer().print(", ");
+                context.emit(invocation.getArguments().get(2));
+                context.writer().print(")");
+                break;
             case "moveMemoryBlock":
                 context.includes().addInclude("<string.h>");
                 context.writer().print("memmove(");

core/src/main/java/org/teavm/backend/c/intrinsic/GCIntrinsic.java

@@ -37,6 +37,8 @@ public class GCIntrinsic implements Intrinsic {
             case "minAvailableBytes":
             case "maxAvailableBytes":
             case "resizeHeap":
+            case "cardTable":
+            case "writeBarrier":
                 return true;
             default:
                 return false;
@@ -45,15 +47,23 @@ public class GCIntrinsic implements Intrinsic {
 
     @Override
     public void apply(IntrinsicContext context, InvocationExpr invocation) {
-        context.includes().includePath("memory.h");
+        switch (invocation.getMethod().getName()) {
-        if (invocation.getMethod().getName().equals("resizeHeap")) {
+            case "resizeHeap":
                 context.writer().print("teavm_gc_resizeHeap(");
                 context.emit(invocation.getArguments().get(0));
                 context.writer().print(")");
-            return;
+                break;
-        }
 
+            case "writeBarrier":
+                context.writer().print("teavm_gc_writeBarrier(");
+                context.emit(invocation.getArguments().get(0));
+                context.writer().print(")");
+                break;
+
+            default:
                 context.includes().includePath("heaptrace.h");
                 context.writer().print("teavm_gc_").print(invocation.getMethod().getName());
+                break;
+        }
     }
 }

core/src/main/java/org/teavm/backend/c/intrinsic/MemoryTraceIntrinsic.java

@@ -27,6 +27,7 @@ public class MemoryTraceIntrinsic implements Intrinsic {
 
     @Override
     public void apply(IntrinsicContext context, InvocationExpr invocation) {
+        context.includes().includePath("heaptrace.h");
         context.writer().print("teavm_gc_").print(invocation.getMethod().getName()).print("(");
         if (!invocation.getArguments().isEmpty()) {
             context.emit(invocation.getArguments().get(0));

core/src/main/java/org/teavm/backend/wasm/WasmHeap.java

@@ -24,7 +24,7 @@ import org.teavm.interop.Unmanaged;
 public final class WasmHeap {
     public static final int PAGE_SIZE = 65536;
     public static final int DEFAULT_STACK_SIZE = PAGE_SIZE * 4;
-    public static final int DEFAULT_REGION_SIZE = 32768;
+    public static final int DEFAULT_REGION_SIZE = 4096;
 
     public static int minHeapSize;
     public static int maxHeapSize;
@@ -33,6 +33,7 @@ public final class WasmHeap {
     public static Address regionsAddress;
     public static int regionsCount;
     public static int regionsSize;
+    public static Address cardTable;
     public static Address heapAddress;
     public static int heapSize;
     public static int regionSize = DEFAULT_REGION_SIZE;
@@ -79,7 +80,8 @@ public final class WasmHeap {
         int newRegionsSize = calculateRegionsSize(newRegionsCount);
 
         Address newRegionsAddress = WasmRuntime.align(heapAddress.add(newHeapSize), 16);
-        Address newStorageAddress = WasmRuntime.align(newRegionsAddress.add(newRegionsSize), 16);
+        Address newCardTable = WasmRuntime.align(newRegionsAddress.add(newRegionsCount), 16);
+        Address newStorageAddress = WasmRuntime.align(newCardTable.add(newRegionsSize), 16);
         Address newMemoryLimit = WasmRuntime.align(newStorageAddress.add(newStorageSize), PAGE_SIZE);
         if (newMemoryLimit != memoryLimit) {
             growMemory((int) (newMemoryLimit.toLong() - memoryLimit.toLong()) / PAGE_SIZE);
@@ -89,11 +91,13 @@ public final class WasmHeap {
             WasmRuntime.moveMemoryBlock(storageAddress, newStorageAddress, storageSize);
         }
         if (regionsSize > 0) {
+            WasmRuntime.moveMemoryBlock(cardTable, newCardTable, regionsCount);
             WasmRuntime.moveMemoryBlock(regionsAddress, newRegionsAddress, regionsSize);
         }
 
         storageAddress = newStorageAddress;
         regionsAddress = newRegionsAddress;
+        cardTable = newCardTable;
         storageSize = newStorageSize;
         regionsCount = newRegionsCount;
         regionsSize = newRegionsSize;

core/src/main/java/org/teavm/backend/wasm/WasmRuntime.java

@@ -97,23 +97,30 @@ public final class WasmRuntime {
     public static native void printOutOfMemory();
 
     public static void fillZero(Address address, int count) {
+        fill(address, (byte) 0, count);
+    }
+
+    public static void fill(Address address, byte value, int count) {
+        int value4 = (value & 0xFF << 24) | (value & 0xFF << 16) | (value & 0xFF << 8) | (value & 0xFF);
         int start = address.toInt();
 
         int alignedStart = start >>> 2 << 2;
         address = Address.fromInt(alignedStart);
         switch (start - alignedStart) {
             case 0:
-                address.putInt(0);
+                address.putInt(value4);
                 break;
             case 1:
-                address.add(1).putByte((byte) 0);
+                address.add(1).putByte(value);
-                address.add(2).putShort((short) 0);
+                address.add(2).putByte(value);
+                address.add(3).putByte(value);
                 break;
             case 2:
-                address.add(2).putShort((short) 0);
+                address.add(2).putByte(value);
+                address.add(3).putByte(value);
                 break;
             case 3:
-                address.add(3).putByte((byte) 0);
+                address.add(3).putByte(value);
                 break;
         }
 
@@ -124,19 +131,21 @@ public final class WasmRuntime {
             case 0:
                 break;
             case 1:
-                address.putByte((byte) 0);
+                address.putByte(value);
                 break;
             case 2:
-                address.putShort((short) 0);
+                address.putByte(value);
+                address.add(1).putByte(value);
                 break;
             case 3:
-                address.putShort((short) 0);
+                address.putByte(value);
-                address.add(2).putByte((byte) 0);
+                address.add(1).putByte(value);
+                address.add(2).putByte(value);
                 break;
         }
 
         for (address = Address.fromInt(alignedStart + 4); address.toInt() < alignedEnd; address = address.add(4)) {
-            address.putInt(0);
+            address.putInt(value4);
         }
     }
 

core/src/main/java/org/teavm/backend/wasm/WasmTarget.java

@@ -272,6 +272,8 @@ public class WasmTarget implements TeaVMTarget, TeaVMWasmHost {
 
         dependencyAnalyzer.linkMethod(new MethodReference(WasmRuntime.class, "align", Address.class, int.class,
                 Address.class)).use();
+        dependencyAnalyzer.linkMethod(new MethodReference(WasmRuntime.class, "fill", Address.class, int.class,
+                int.class, void.class)).use();
         dependencyAnalyzer.linkMethod(new MethodReference(WasmRuntime.class, "fillZero", Address.class, int.class,
                 void.class)).use();
         dependencyAnalyzer.linkMethod(new MethodReference(WasmRuntime.class, "moveMemoryBlock", Address.class,
@@ -821,6 +823,7 @@ public class WasmTarget implements TeaVMTarget, TeaVMWasmHost {
         address = WasmRuntime.align(address + WasmHeap.DEFAULT_STACK_SIZE, 16);
         address = WasmRuntime.align(address + maxHeapSize, 16);
         address = WasmRuntime.align(address + newRegionsSize, 16);
+        address = WasmRuntime.align(address + newRegionsCount, 16);
         address = WasmRuntime.align(address + newStorageSize, 16);
         gcIntrinsic.setRegionSize(WasmHeap.DEFAULT_REGION_SIZE);
 

core/src/main/java/org/teavm/backend/wasm/intrinsics/AllocatorIntrinsic.java

@@ -46,6 +46,7 @@ public class AllocatorIntrinsic implements WasmIntrinsic {
             return false;
         }
         switch (methodReference.getName()) {
+            case "fill":
             case "fillZero":
             case "moveMemoryBlock":
             case "isInitialized":
@@ -58,6 +59,7 @@ public class AllocatorIntrinsic implements WasmIntrinsic {
     @Override
     public WasmExpression apply(InvocationExpr invocation, WasmIntrinsicManager manager) {
         switch (invocation.getMethod().getName()) {
+            case "fill":
             case "fillZero":
             case "moveMemoryBlock": {
                 MethodReference delegateMethod = new MethodReference(WasmRuntime.class.getName(),

core/src/main/java/org/teavm/backend/wasm/intrinsics/GCIntrinsic.java

@@ -27,7 +27,11 @@ import org.teavm.backend.wasm.model.expression.WasmConversion;
 import org.teavm.backend.wasm.model.expression.WasmExpression;
 import org.teavm.backend.wasm.model.expression.WasmInt32Constant;
 import org.teavm.backend.wasm.model.expression.WasmInt32Subtype;
+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.WasmLoadInt32;
+import org.teavm.backend.wasm.model.expression.WasmStoreInt32;
 import org.teavm.backend.wasm.model.expression.WasmUnreachable;
 import org.teavm.model.FieldReference;
 import org.teavm.model.MethodReference;
@@ -38,6 +42,8 @@ public class GCIntrinsic implements WasmIntrinsic {
             WasmRuntime.class, "printOutOfMemory", void.class);
     private static final MethodReference RESIZE_HEAP = new MethodReference(
             WasmHeap.class, "resizeHeap", int.class, void.class);
+    private static final FieldReference CARD_TABLE = new FieldReference(WasmHeap.class.getName(), "cardTable");
+    private static final FieldReference HEAP_ADDRESS = new FieldReference(WasmHeap.class.getName(), "heapAddress");
     private List<WasmInt32Constant> regionSizeExpressions = new ArrayList<>();
 
     public void setRegionSize(int regionSize) {
@@ -58,12 +64,14 @@ public class GCIntrinsic implements WasmIntrinsic {
             case "heapAddress":
             case "availableBytes":
             case "regionsAddress":
+            case "cardTable":
             case "regionMaxCount":
             case "regionSize":
             case "outOfMemory":
             case "minAvailableBytes":
             case "maxAvailableBytes":
             case "resizeHeap":
+            case "writeBarrier":
                 return true;
             default:
                 return false;
@@ -81,6 +89,8 @@ public class GCIntrinsic implements WasmIntrinsic {
                 return getStaticField(manager, "heapAddress");
             case "regionsAddress":
                 return getStaticField(manager, "regionsAddress");
+            case "cardTable":
+                return getStaticField(manager, "cardTable");
             case "regionMaxCount":
                 return getStaticField(manager, "regionsCount");
             case "minAvailableBytes":
@@ -106,6 +116,21 @@ public class GCIntrinsic implements WasmIntrinsic {
                 block.getBody().add(new WasmUnreachable());
                 return block;
             }
+            case "writeBarrier": {
+                WasmExpression cardTableField = new WasmInt32Constant(manager.getStaticField(CARD_TABLE));
+                WasmExpression cardTable = new WasmLoadInt32(4, cardTableField, WasmInt32Subtype.INT32);
+                WasmExpression heapAddressField = new WasmInt32Constant(manager.getStaticField(HEAP_ADDRESS));
+                WasmExpression heapAddress = new WasmLoadInt32(4, heapAddressField, WasmInt32Subtype.INT32);
+                WasmInt32Constant regionSize = new WasmInt32Constant(0);
+                regionSizeExpressions.add(regionSize);
+                WasmExpression offsetInHeap = new WasmIntBinary(WasmIntType.INT32, WasmIntBinaryOperation.SUB,
+                        manager.generate(invocation.getArguments().get(0)), heapAddress);
+                WasmExpression cardIndex = new WasmIntBinary(WasmIntType.INT32, WasmIntBinaryOperation.DIV_SIGNED,
+                        offsetInHeap, regionSize);
+                WasmExpression card = new WasmIntBinary(WasmIntType.INT32, WasmIntBinaryOperation.ADD, cardTable,
+                        cardIndex);
+                return new WasmStoreInt32(1, card, new WasmInt32Constant(0), WasmInt32Subtype.INT8);
+            }
             default:
                 throw new IllegalArgumentException(invocation.getMethod().toString());
         }

core/src/main/java/org/teavm/dependency/Linker.java

@@ -23,23 +23,23 @@ import org.teavm.model.ElementModifier;
 import org.teavm.model.FieldHolder;
 import org.teavm.model.FieldReference;
 import org.teavm.model.Instruction;
-import org.teavm.model.MethodDescriptor;
 import org.teavm.model.MethodHolder;
 import org.teavm.model.MethodReader;
 import org.teavm.model.MethodReference;
 import org.teavm.model.Program;
 import org.teavm.model.instructions.GetFieldInstruction;
-import org.teavm.model.instructions.InitClassInstruction;
 import org.teavm.model.instructions.InvocationType;
 import org.teavm.model.instructions.InvokeInstruction;
 import org.teavm.model.instructions.PutFieldInstruction;
+import org.teavm.model.transformation.ClassInitInsertion;
 
 public class Linker {
-    private static final MethodDescriptor clinitDescriptor = new MethodDescriptor("<clinit>", void.class);
     private DependencyInfo dependency;
+    private ClassInitInsertion classInitInsertion;
 
     public Linker(DependencyInfo dependency) {
         this.dependency = dependency;
+        classInitInsertion = new ClassInitInsertion(dependency);
     }
 
     public void link(ClassHolder cls) {
@@ -55,7 +55,7 @@ public class Linker {
                     method.setProgram(null);
                 }
             } else if (method.getProgram() != null) {
-                link(method.getReference(), method.getProgram());
+                link(method, method.getProgram());
             }
         }
         for (FieldHolder field : cls.getFields().toArray(new FieldHolder[0])) {
@@ -66,7 +66,7 @@ public class Linker {
         }
     }
 
-    public void link(MethodReference method, Program program) {
+    public void link(MethodReader method, Program program) {
         for (int i = 0; i < program.basicBlockCount(); ++i) {
             BasicBlock block = program.basicBlockAt(i);
             for (Instruction insn : block) {
@@ -111,36 +111,16 @@ public class Linker {
                         getField.setField(linkedField.getReference());
                     }
 
-                    FieldReference fieldRef = getField.getField();
-                    if (getField.getInstance() == null) {
-                        insertClinit(dependency, fieldRef.getClassName(), method, insn);
-                    }
                 } else if (insn instanceof PutFieldInstruction) {
                     PutFieldInstruction putField = (PutFieldInstruction) insn;
                     FieldDependencyInfo linkedField = dependency.getField(putField.getField());
                     if (linkedField != null) {
                         putField.setField(linkedField.getReference());
                     }
-
-                    FieldReference fieldRef = putField.getField();
-                    if (putField.getInstance() == null) {
-                        insertClinit(dependency, fieldRef.getClassName(), method, insn);
-                    }
-                }
                 }
             }
         }
 
-    private void insertClinit(DependencyInfo dependency, String className, MethodReference method, Instruction insn) {
+        classInitInsertion.apply(program, method);
-        if (className.equals(method.getClassName())) {
-            return;
-        }
-        ClassReader cls = dependency.getClassSource().get(className);
-        if (cls == null || cls.getMethod(clinitDescriptor) != null) {
-            InitClassInstruction initInsn = new InitClassInstruction();
-            initInsn.setClassName(className);
-            initInsn.setLocation(insn.getLocation());
-            insn.insertPrevious(initInsn);
-        }
     }
 }

core/src/main/java/org/teavm/model/lowlevel/GCShadowStackContributor.java

@@ -33,14 +33,13 @@ 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;
 import org.teavm.model.MethodReader;
 import org.teavm.model.MethodReference;
-import org.teavm.model.Phi;
 import org.teavm.model.Program;
 import org.teavm.model.Variable;
 import org.teavm.model.instructions.AssignInstruction;
+import org.teavm.model.instructions.CastInstruction;
 import org.teavm.model.instructions.ClassConstantInstruction;
 import org.teavm.model.instructions.IntegerConstantInstruction;
 import org.teavm.model.instructions.InvocationType;
@@ -48,6 +47,7 @@ import org.teavm.model.instructions.InvokeInstruction;
 import org.teavm.model.instructions.NullCheckInstruction;
 import org.teavm.model.instructions.NullConstantInstruction;
 import org.teavm.model.instructions.StringConstantInstruction;
+import org.teavm.model.instructions.UnwrapArrayInstruction;
 import org.teavm.model.util.DefinitionExtractor;
 import org.teavm.model.util.GraphColorer;
 import org.teavm.model.util.LivenessAnalyzer;
@@ -98,28 +98,38 @@ public class GCShadowStackContributor {
         // for this phi.
         Graph cfg = ProgramUtils.buildControlFlowGraph(program);
         DominatorTree dom = GraphUtils.buildDominatorTree(cfg);
-        boolean[] autoSpilled = new SpilledPhisFinder(liveInInformation, dom, program).find();
+        boolean[] autoSpilled = new SpilledPhisFinder(liveInInformation, dom, program, variableClasses, colors).find();
 
         List<Map<Instruction, int[]>> liveInStores = reduceGCRootStores(dom, program, usedColors, liveInInformation,
-                colors, autoSpilled);
+                colors, autoSpilled, variableClasses);
         putLiveInGCRoots(program, liveInStores);
 
         return usedColors;
     }
 
     private int[] getVariableClasses(Program program) {
-        DisjointSet variableClasses = new DisjointSet();
+        DisjointSet disjointSet = new DisjointSet();
         for (int i = 0; i < program.variableCount(); ++i) {
-            variableClasses.create();
+            disjointSet.create();
         }
         for (BasicBlock block : program.getBasicBlocks()) {
-            for (Phi phi : block.getPhis()) {
+            for (Instruction instruction : block) {
-                for (Incoming incoming : phi.getIncomings()) {
+                if (instruction instanceof AssignInstruction) {
-                    variableClasses.union(phi.getReceiver().getIndex(), incoming.getValue().getIndex());
+                    AssignInstruction assign = (AssignInstruction) instruction;
+                    disjointSet.union(assign.getAssignee().getIndex(), assign.getReceiver().getIndex());
+                } else if (instruction instanceof NullCheckInstruction) {
+                    NullCheckInstruction nullCheck = (NullCheckInstruction) instruction;
+                    disjointSet.union(nullCheck.getValue().getIndex(), nullCheck.getReceiver().getIndex());
+                } else if (instruction instanceof CastInstruction) {
+                    CastInstruction cast = (CastInstruction) instruction;
+                    disjointSet.union(cast.getValue().getIndex(), cast.getReceiver().getIndex());
+                } else if (instruction instanceof UnwrapArrayInstruction) {
+                    UnwrapArrayInstruction unwrapArray = (UnwrapArrayInstruction) instruction;
+                    disjointSet.union(unwrapArray.getArray().getIndex(), unwrapArray.getReceiver().getIndex());
                 }
             }
         }
-        return variableClasses.pack(program.variableCount());
+        return disjointSet.pack(program.variableCount());
     }
 
     private List<Map<Instruction, BitSet>> findCallSiteLiveIns(Program program, MethodReader method) {
@@ -207,7 +217,8 @@ public class GCShadowStackContributor {
     }
 
     private List<Map<Instruction, int[]>> reduceGCRootStores(DominatorTree dom, Program program, int usedColors,
-            List<Map<Instruction, BitSet>> liveInInformation, int[] colors, boolean[] autoSpilled) {
+            List<Map<Instruction, BitSet>> liveInInformation, int[] colors, boolean[] autoSpilled,
+            int[] variableClasses) {
         class Step {
             private final int node;
             private final int[] slotStates = new int[usedColors];
@@ -228,7 +239,6 @@ public class GCShadowStackContributor {
         Step start = new Step(0);
         Arrays.fill(start.slotStates, program.variableCount());
         stack[head++] = start;
-        int[] definitionClasses = getDefinitionClasses(program);
 
         while (head > 0) {
             Step step = stack[--head];
@@ -250,7 +260,7 @@ public class GCShadowStackContributor {
                     }
                 }
 
-                int[] updates = compareStates(previousStates, states, autoSpilled, definitionClasses);
+                int[] updates = compareStates(previousStates, states, autoSpilled, variableClasses);
                 updatesByCallSite.put(callSiteLocation, updates);
                 previousStates = states;
                 states = states.clone();
@@ -266,22 +276,6 @@ public class GCShadowStackContributor {
         return slotsToUpdate;
     }
 
-    private int[] getDefinitionClasses(Program program) {
-        DisjointSet disjointSet = new DisjointSet();
-        for (int i = 0; i < program.variableCount(); ++i) {
-            disjointSet.create();
-        }
-        for (BasicBlock block : program.getBasicBlocks()) {
-            for (Instruction instruction : block) {
-                if (instruction instanceof NullCheckInstruction) {
-                    NullCheckInstruction nullCheck = (NullCheckInstruction) instruction;
-                    disjointSet.union(nullCheck.getValue().getIndex(), nullCheck.getReceiver().getIndex());
-                }
-            }
-        }
-        return disjointSet.pack(program.variableCount());
-    }
-
     private List<Instruction> sortInstructions(Collection<Instruction> instructions, BasicBlock block) {
         ObjectIntMap<Instruction> indexes = new ObjectIntHashMap<>();
         int index = 0;

core/src/main/java/org/teavm/model/lowlevel/SpilledPhisFinder.java

@@ -37,26 +37,33 @@ class SpilledPhisFinder {
     int[][] variableSpilledBlocks;
     Phi[] definingPhis;
     int variableCount;
+    private int[] variableClasses;
+    private int[] colors;
 
-    SpilledPhisFinder(List<Map<Instruction, BitSet>> liveInInformation, DominatorTree dom, Program program) {
+    SpilledPhisFinder(List<Map<Instruction, BitSet>> liveInInformation, DominatorTree dom, Program program,
+            int[] variableClasses, int[] colors) {
         this.dom = dom;
         variableCount = program.variableCount();
         autoSpilled = new boolean[variableCount];
         status = new byte[variableCount];
-        variableSpilledBlocks = variableSpilledBlocks(liveInInformation, variableCount);
+        variableSpilledBlocks = variableSpilledBlocks(liveInInformation, variableCount, variableClasses);
-        definingPhis = findPhis(program);
+        definingPhis = findPhis(program, variableClasses);
+        this.variableClasses = variableClasses;
+        this.colors = colors;
     }
 
-    private static int[][] variableSpilledBlocks(List<Map<Instruction, BitSet>> liveInInformation, int count) {
+    private static int[][] variableSpilledBlocks(List<Map<Instruction, BitSet>> liveInInformation, int count,
+            int[] variableClasses) {
         IntSet[] builder = new IntSet[count];
         for (int b = 0; b < liveInInformation.size(); b++) {
             Map<Instruction, BitSet> blockLiveIn = liveInInformation.get(b);
             for (BitSet liveVarsSet : blockLiveIn.values()) {
                 for (int v = liveVarsSet.nextSetBit(0); v >= 0; v = liveVarsSet.nextSetBit(v + 1)) {
-                    if (builder[v] == null) {
+                    int cls = variableClasses[v];
-                        builder[v] = new IntHashSet();
+                    if (builder[cls] == null) {
+                        builder[cls] = new IntHashSet();
                     }
-                    builder[v].add(b);
+                    builder[cls].add(b);
                 }
             }
         }
@@ -71,11 +78,11 @@ class SpilledPhisFinder {
         return result;
     }
 
-    private static Phi[] findPhis(Program program) {
+    private static Phi[] findPhis(Program program, int[] variableClasses) {
         Phi[] result = new Phi[program.variableCount()];
         for (BasicBlock block : program.getBasicBlocks()) {
             for (Phi phi : block.getPhis()) {
-                result[phi.getReceiver().getIndex()] = phi;
+                result[variableClasses[phi.getReceiver().getIndex()]] = phi;
             }
         }
         return result;
@@ -89,6 +96,8 @@ class SpilledPhisFinder {
     }
 
     private boolean isAutoSpilled(int v) {
+        v = variableClasses[v];
+
         if (status[v] == VISITED) {
             return autoSpilled[v];
         }
@@ -107,6 +116,10 @@ class SpilledPhisFinder {
 
         boolean result = true;
         for (Incoming incoming : definingPhi.getIncomings()) {
+            if (colors[incoming.getValue().getIndex()] != colors[definingPhi.getReceiver().getIndex()]) {
+                result = false;
+                break;
+            }
             if (!isAutoSpilled(incoming.getValue().getIndex())) {
                 int[] spilledAt = variableSpilledBlocks[incoming.getValue().getIndex()];
                 result = false;

core/src/main/java/org/teavm/model/lowlevel/WriteBarrierInsertion.java

@@ -0,0 +1,236 @@
+/*
+ *  Copyright 2019 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.lowlevel;
+
+import com.carrotsearch.hppc.IntArrayList;
+import com.carrotsearch.hppc.IntHashSet;
+import com.carrotsearch.hppc.IntSet;
+import com.carrotsearch.hppc.cursors.IntCursor;
+import org.teavm.model.BasicBlock;
+import org.teavm.model.Instruction;
+import org.teavm.model.MethodReference;
+import org.teavm.model.Phi;
+import org.teavm.model.Program;
+import org.teavm.model.ValueType;
+import org.teavm.model.Variable;
+import org.teavm.model.instructions.AbstractInstructionVisitor;
+import org.teavm.model.instructions.ArrayElementType;
+import org.teavm.model.instructions.AssignInstruction;
+import org.teavm.model.instructions.CastInstruction;
+import org.teavm.model.instructions.CloneArrayInstruction;
+import org.teavm.model.instructions.ConstructArrayInstruction;
+import org.teavm.model.instructions.ConstructInstruction;
+import org.teavm.model.instructions.ConstructMultiArrayInstruction;
+import org.teavm.model.instructions.InitClassInstruction;
+import org.teavm.model.instructions.InvocationType;
+import org.teavm.model.instructions.InvokeInstruction;
+import org.teavm.model.instructions.MonitorEnterInstruction;
+import org.teavm.model.instructions.MonitorExitInstruction;
+import org.teavm.model.instructions.NullCheckInstruction;
+import org.teavm.model.instructions.PutElementInstruction;
+import org.teavm.model.instructions.PutFieldInstruction;
+import org.teavm.model.util.DominatorWalker;
+import org.teavm.model.util.DominatorWalkerCallback;
+import org.teavm.model.util.DominatorWalkerContext;
+import org.teavm.runtime.GC;
+import org.teavm.runtime.RuntimeObject;
+
+public class WriteBarrierInsertion {
+    private static final MethodReference BARRIER_METHOD = new MethodReference(GC.class, "writeBarrier",
+            RuntimeObject.class, void.class);
+    private Characteristics characteristics;
+
+    public WriteBarrierInsertion(Characteristics characteristics) {
+        this.characteristics = characteristics;
+    }
+
+    public void apply(Program program) {
+        if (program.basicBlockCount() == 0) {
+            return;
+        }
+        new DominatorWalker(program).walk(new WalkerCallbackImpl());
+    }
+
+    class WalkerCallbackImpl extends AbstractInstructionVisitor implements DominatorWalkerCallback<State> {
+        private DominatorWalkerContext context;
+        IntHashSet installedBarriers = new IntHashSet();
+        State state;
+
+        @Override
+        public void setContext(DominatorWalkerContext context) {
+            this.context = context;
+        }
+
+        @Override
+        public State visit(BasicBlock block) {
+            state = new State();
+
+            if (context.isExceptionHandler(block.getIndex()) || !context.allPredecessorsVisited(block.getIndex())) {
+                invalidateBarriers();
+            } else {
+                for (Phi phi : block.getPhis()) {
+                    if (phi.getIncomings().stream().allMatch(
+                            incoming -> installedBarriers.contains(incoming.getValue().getIndex()))) {
+                        markAsInstalled(phi.getReceiver().getIndex());
+                    }
+                }
+            }
+
+            for (Instruction instruction : block) {
+                instruction.acceptVisitor(this);
+            }
+
+            return state;
+        }
+
+        @Override
+        public void endVisit(BasicBlock block, State state) {
+            if (state.oldBarriers != null) {
+                installedBarriers.clear();
+                installedBarriers.addAll(state.oldBarriers);
+            } else {
+                for (IntCursor cursor : state.newBarriers) {
+                    installedBarriers.remove(cursor.value);
+                }
+            }
+        }
+
+        @Override
+        public void visit(PutFieldInstruction insn) {
+            if (insn.getInstance() != null && isManagedReferenceType(insn.getFieldType())) {
+                installBarrier(insn, insn.getInstance());
+            }
+        }
+
+        @Override
+        public void visit(InvokeInstruction insn) {
+            invalidateBarriers();
+        }
+
+        @Override
+        public void visit(ConstructInstruction insn) {
+            invalidateBarriers();
+            markAsInstalled(insn.getReceiver().getIndex());
+        }
+
+        @Override
+        public void visit(InitClassInstruction insn) {
+            invalidateBarriers();
+        }
+
+        @Override
+        public void visit(CloneArrayInstruction insn) {
+            invalidateBarriers();
+        }
+
+        @Override
+        public void visit(ConstructArrayInstruction insn) {
+            invalidateBarriers();
+        }
+
+        @Override
+        public void visit(ConstructMultiArrayInstruction insn) {
+            invalidateBarriers();
+        }
+
+        @Override
+        public void visit(MonitorEnterInstruction insn) {
+            invalidateBarriers();
+        }
+
+        @Override
+        public void visit(MonitorExitInstruction insn) {
+            invalidateBarriers();
+        }
+
+        private boolean isManagedReferenceType(ValueType type) {
+            if (type instanceof ValueType.Array) {
+                return true;
+            }
+            if (type instanceof ValueType.Object) {
+                return characteristics.isManaged(((ValueType.Object) type).getClassName());
+            }
+            return false;
+        }
+
+        @Override
+        public void visit(PutElementInstruction insn) {
+            if (insn.getType() == ArrayElementType.OBJECT) {
+                installBarrier(insn, insn.getArray());
+            }
+        }
+
+        @Override
+        public void visit(AssignInstruction insn) {
+            assign(insn.getAssignee(), insn.getReceiver());
+        }
+
+        @Override
+        public void visit(CastInstruction insn) {
+            assign(insn.getValue(), insn.getReceiver());
+        }
+
+        @Override
+        public void visit(NullCheckInstruction insn) {
+            assign(insn.getValue(), insn.getReceiver());
+        }
+
+        private void assign(Variable from, Variable to) {
+            if (installedBarriers.contains(from.getIndex())) {
+                markAsInstalled(to.getIndex());
+            }
+        }
+
+        private void installBarrier(Instruction instruction, Variable variable) {
+            if (markAsInstalled(variable.getIndex())) {
+                InvokeInstruction invoke = new InvokeInstruction();
+                invoke.setType(InvocationType.SPECIAL);
+                invoke.setMethod(BARRIER_METHOD);
+                invoke.setArguments(variable);
+                invoke.setLocation(instruction.getLocation());
+                instruction.insertPrevious(invoke);
+            }
+        }
+
+        private boolean markAsInstalled(int index) {
+            if (!installedBarriers.add(index)) {
+                return false;
+            }
+            if (state.newBarriers != null) {
+                state.newBarriers.add(index);
+            }
+            return true;
+        }
+
+        private void invalidateBarriers() {
+            if (state.newBarriers != null) {
+                state.oldBarriers = new IntArrayList();
+                for (IntCursor cursor : installedBarriers) {
+                    if (!state.newBarriers.contains(cursor.value)) {
+                        state.oldBarriers.add(cursor.value);
+                    }
+                }
+                state.newBarriers = null;
+            }
+            installedBarriers.clear();
+        }
+    }
+
+    static class State {
+        IntSet newBarriers = new IntHashSet();
+        IntArrayList oldBarriers;
+    }
+}

core/src/main/java/org/teavm/model/transformation/ClassInitInsertion.java

@@ -0,0 +1,168 @@
+/*
+ *  Copyright 2019 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.transformation;
+
+import java.util.HashSet;
+import java.util.Set;
+import org.teavm.dependency.DependencyInfo;
+import org.teavm.model.BasicBlock;
+import org.teavm.model.ClassReader;
+import org.teavm.model.ElementModifier;
+import org.teavm.model.Instruction;
+import org.teavm.model.MethodDescriptor;
+import org.teavm.model.MethodReader;
+import org.teavm.model.Program;
+import org.teavm.model.instructions.AbstractInstructionVisitor;
+import org.teavm.model.instructions.GetFieldInstruction;
+import org.teavm.model.instructions.InitClassInstruction;
+import org.teavm.model.instructions.InvokeInstruction;
+import org.teavm.model.instructions.PutFieldInstruction;
+import org.teavm.model.util.DominatorWalker;
+import org.teavm.model.util.DominatorWalkerCallback;
+import org.teavm.model.util.DominatorWalkerContext;
+
+public class ClassInitInsertion {
+    private static final MethodDescriptor CLINIT = new MethodDescriptor("<clinit>", void.class);
+    private DependencyInfo dependencyInfo;
+
+    public ClassInitInsertion(DependencyInfo dependencyInfo) {
+        this.dependencyInfo = dependencyInfo;
+    }
+
+    public void apply(Program program, MethodReader method) {
+        if (program.basicBlockCount() == 0) {
+            return;
+        }
+        String currentClass = null;
+        if (method.hasModifier(ElementModifier.STATIC)) {
+            currentClass = method.getOwnerName();
+        }
+        Visitor visitor = new Visitor(currentClass);
+        new DominatorWalker(program).walk(visitor);
+    }
+
+    class Visitor extends AbstractInstructionVisitor implements DominatorWalkerCallback<State> {
+        private String currentClass;
+        private DominatorWalkerContext context;
+        Set<String> initializedClasses = new HashSet<>();
+        private State state;
+
+        Visitor(String currentClass) {
+            this.currentClass = currentClass;
+            if (currentClass != null) {
+                initializedClasses.add(currentClass);
+            }
+        }
+
+        @Override
+        public void setContext(DominatorWalkerContext context) {
+            this.context = context;
+        }
+
+        @Override
+        public State visit(BasicBlock block) {
+            state = new State();
+            if (context.isExceptionHandler(block.getIndex())) {
+                markAllClassesAsNotInitialized();
+                if (currentClass != null) {
+                    markClassAsInitialized(currentClass);
+                }
+            }
+
+            for (Instruction instruction : block) {
+                instruction.acceptVisitor(this);
+            }
+
+            return state;
+        }
+
+        @Override
+        public void endVisit(BasicBlock block, State state) {
+            if (state.oldInitializedClasses != null) {
+                initializedClasses.clear();
+                initializedClasses.addAll(state.oldInitializedClasses);
+            } else {
+                initializedClasses.removeAll(state.newInitializedClasses);
+            }
+        }
+
+        @Override
+        public void visit(GetFieldInstruction insn) {
+            if (insn.getInstance() == null) {
+                initializeClass(insn.getField().getClassName(), insn);
+            }
+        }
+
+        @Override
+        public void visit(PutFieldInstruction insn) {
+            if (insn.getInstance() == null) {
+                initializeClass(insn.getField().getClassName(), insn);
+            }
+        }
+
+        @Override
+        public void visit(InvokeInstruction insn) {
+            if (insn.getInstance() == null) {
+                markClassAsInitialized(insn.getMethod().getClassName());
+            }
+        }
+
+        @Override
+        public void visit(InitClassInstruction insn) {
+            markClassAsInitialized(insn.getClassName());
+        }
+
+        private void initializeClass(String className, Instruction instruction) {
+            if (markClassAsInitialized(className)) {
+                ClassReader cls = dependencyInfo.getClassSource().get(className);
+                if (cls == null || cls.getMethod(CLINIT) != null) {
+                    InitClassInstruction initInsn = new InitClassInstruction();
+                    initInsn.setClassName(className);
+                    initInsn.setLocation(instruction.getLocation());
+                    instruction.insertPrevious(initInsn);
+                }
+            }
+        }
+
+        boolean markClassAsInitialized(String className) {
+            if (initializedClasses.add(className)) {
+                if (state.newInitializedClasses != null) {
+                    state.newInitializedClasses.add(className);
+                }
+                return true;
+            }
+            return false;
+        }
+
+        private void markAllClassesAsNotInitialized() {
+            if (state.newInitializedClasses != null) {
+                state.oldInitializedClasses = new HashSet<>();
+                for (String className : initializedClasses) {
+                    if (!state.newInitializedClasses.contains(className)) {
+                        state.oldInitializedClasses.add(className);
+                    }
+                }
+                state.newInitializedClasses = null;
+            }
+            initializedClasses.clear();
+        }
+    }
+
+    static class State {
+        Set<String> newInitializedClasses = new HashSet<>();
+        Set<String> oldInitializedClasses;
+    }
+}

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

@@ -15,29 +15,70 @@
  */
 package org.teavm.model.util;
 
+import com.carrotsearch.hppc.IntStack;
 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;
+import org.teavm.model.TryCatchBlock;
 
 public class DominatorWalker {
     private Program program;
     private DominatorTree dom;
+    private Graph cfg;
     private Graph domGraph;
+    private int[] order;
 
     public DominatorWalker(Program program) {
         this.program = program;
-        Graph cfg = ProgramUtils.buildControlFlowGraph(program);
+        cfg = ProgramUtils.buildControlFlowGraph(program);
         dom = GraphUtils.buildDominatorTree(cfg);
         domGraph = GraphUtils.buildDominatorGraph(dom, cfg.size());
+        order = dfs(cfg);
+    }
+
+    private int[] dfs(Graph graph) {
+        if (graph.size() == 0) {
+            return new int[0];
+        }
+
+        int index = 0;
+        int[] result = new int[graph.size()];
+        IntStack stack = new IntStack(graph.size());
+        byte[] state = new byte[graph.size()];
+        stack.push(0);
+
+        while (!stack.isEmpty()) {
+            int node = stack.pop();
+            switch (state[node]) {
+                case 0: {
+                    state[node] = 1;
+                    stack.push(node);
+                    for (int succ : graph.outgoingEdges(node)) {
+                        if (state[succ] == 0) {
+                            stack.push(succ);
+                        }
+                    }
+                    break;
+                }
+                case 1: {
+                    state[node] = 2;
+                    result[node] = index++;
+                    break;
+                }
+            }
+        }
+
+        return result;
     }
 
     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];
-        callback.setDomTree(dom);
+        ContextImpl context = new ContextImpl(dom, cfg, findExceptionHandlers());
+        callback.setContext(context);
 
         int head = 1;
         while (head > 0) {
@@ -47,6 +88,7 @@ public class DominatorWalker {
                 @SuppressWarnings("unchecked")
                 T state = (T) stateStack[head];
                 callback.endVisit(block, state);
+                context.visited[block.getIndex()] = true;
             } else if (callback.filter(block)) {
                 stack[head] = node;
                 backward[head] = true;
@@ -54,6 +96,7 @@ public class DominatorWalker {
                 head++;
 
                 int[] successors = domGraph.outgoingEdges(node);
+                sort(successors);
                 for (int i = successors.length - 1; i >= 0; --i) {
                     stack[head] = successors[i];
                     backward[head] = false;
@@ -62,4 +105,69 @@ public class DominatorWalker {
             }
         }
     }
+
+    private boolean[] findExceptionHandlers() {
+        boolean[] exceptionHandlers = new boolean[program.basicBlockCount()];
+        for (BasicBlock block : program.getBasicBlocks()) {
+            for (TryCatchBlock tryCatch : block.getTryCatchBlocks()) {
+                exceptionHandlers[tryCatch.getHandler().getIndex()] = true;
+            }
+        }
+        return exceptionHandlers;
+    }
+
+    private void sort(int[] nodes) {
+        for (int i = 0; i < nodes.length - 1; ++i) {
+            int a = nodes[i];
+            int bestIndex = i;
+            int best = order[a];
+            for (int j = i + 1; j < nodes.length; ++j) {
+                int b = nodes[j];
+                int score = order[b];
+                if (score < best) {
+                    best = score;
+                    a = b;
+                    bestIndex = j;
+                }
+            }
+            if (i != bestIndex) {
+                nodes[bestIndex] = nodes[i];
+                nodes[i] = a;
+            }
+        }
+    }
+
+    static class ContextImpl implements DominatorWalkerContext {
+        private boolean[] visited;
+        private boolean[] isExceptionHandler;
+        private DominatorTree dom;
+        private Graph cfg;
+
+        ContextImpl(DominatorTree dom, Graph cfg, boolean[] isExceptionHandler) {
+            this.dom = dom;
+            this.cfg = cfg;
+            this.isExceptionHandler = isExceptionHandler;
+            visited = new boolean[cfg.size()];
+        }
+
+        @Override
+        public DominatorTree getDominatorTree() {
+            return dom;
+        }
+
+        @Override
+        public Graph getControlFlowGraph() {
+            return cfg;
+        }
+
+        @Override
+        public boolean isVisited(int blockIndex) {
+            return visited[blockIndex];
+        }
+
+        @Override
+        public boolean isExceptionHandler(int blockIndex) {
+            return isExceptionHandler[blockIndex];
+        }
+    }
 }

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

@@ -15,7 +15,6 @@
  */
 package org.teavm.model.util;
 
-import org.teavm.common.DominatorTree;
 import org.teavm.model.BasicBlock;
 
 /**
@@ -24,7 +23,7 @@ import org.teavm.model.BasicBlock;
  * @param <T> type of state that can be saved for each visited node.
  */
 public interface DominatorWalkerCallback<T> {
-    default void setDomTree(DominatorTree domTree) {
+    default void setContext(DominatorWalkerContext context) {
     }
 
     /**

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

@@ -0,0 +1,38 @@
+/*
+ *  Copyright 2019 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;
+
+public interface DominatorWalkerContext {
+    DominatorTree getDominatorTree();
+
+    Graph getControlFlowGraph();
+
+    boolean isVisited(int blockIndex);
+
+    boolean isExceptionHandler(int blockIndex);
+
+    default boolean allPredecessorsVisited(int blockIndex) {
+        for (int predecessor : getControlFlowGraph().incomingEdges(blockIndex)) {
+            if (!isVisited(predecessor)) {
+                return false;
+            }
+        }
+        return true;
+    }
+}

core/src/main/java/org/teavm/runtime/Allocator.java

@@ -21,6 +21,7 @@ import org.teavm.interop.Structure;
 import org.teavm.interop.Unmanaged;
 
 @StaticInit
+@Unmanaged
 public final class Allocator {
     private Allocator() {
     }
@@ -62,12 +63,11 @@ public final class Allocator {
         return array;
     }
 
-    @Unmanaged
     public static native void fillZero(Address address, int count);
 
-    @Unmanaged
+    public static native void fill(Address address, byte value, int count);
+
     public static native void moveMemoryBlock(Address source, Address target, int count);
 
-    @Unmanaged
     public static native boolean isInitialized(Class<?> cls);
 }

core/src/main/java/org/teavm/runtime/MemoryTrace.java

@@ -29,17 +29,27 @@ public class MemoryTrace {
 
     public static native void checkIsFree(Address address, int size);
 
-    public static native void initMark();
+    public static native void markStarted();
 
     public static native void mark(Address address);
 
+    public static native void reportDirtyRegion(Address address);
+
+    public static native void markCompleted();
+
     public static native void move(Address from, Address to, int size);
 
-    public static native void gcStarted();
+    public static native void gcStarted(boolean full);
+
+    public static native void sweepStarted();
 
     public static native void sweepCompleted();
 
+    public static native void defragStarted();
+
     public static native void defragCompleted();
 
     public static native void writeHeapDump();
+
+    public static native void gcCompleted();
 }

core/src/main/java/org/teavm/runtime/RuntimeObject.java

@@ -21,6 +21,7 @@ import org.teavm.interop.Structure;
 @StaticInit
 public class RuntimeObject extends Structure {
     public static final int GC_MARKED = 0x80000000;
+    public static final int GC_OLD_GENERATION = 0x40000000;
 
     public static int nextId;
 

core/src/main/java/org/teavm/vm/TeaVM.java

@@ -961,7 +961,7 @@ public class TeaVM implements TeaVMHost, ServiceRepository {
                     if (program == null) {
                         program = ProgramUtils.copy(classReader.getMethod(method.getDescriptor()).getProgram());
                         missingItemsProcessor.processMethod(method.getReference(), program);
-                        linker.link(method.getReference(), program);
+                        linker.link(method, program);
                         clinitInsertion.apply(method, program);
                         program = optimizeMethodCacheMiss(method, program);
                         Program finalProgram = program;

core/src/main/resources/org/teavm/backend/c/core.h

@@ -180,3 +180,9 @@ extern TeaVM_Class* teavm_stringClass;
 extern TeaVM_Class* teavm_charArrayClass;
 extern int32_t teavm_classReferencesCount;
 extern void teavm_initClasses();
+
+
+inline static void teavm_gc_writeBarrier(void* object) {
+    intptr_t offset = (intptr_t) ((char*) object - (char*) teavm_gc_heapAddress) / teavm_gc_regionSize;
+    ((char*) teavm_gc_cardTable)[offset] = 0;
+}

core/src/main/resources/org/teavm/backend/c/definitions.h

@@ -59,6 +59,10 @@
     #define TEAVM_GC_LOG 0
 #endif
 
+#ifndef TEAVM_GC_STATS
+    #define TEAVM_GC_STATS 0
+#endif
+
 #ifndef TEAVM_OBFUSCATED
     #define TEAVM_OBFUSCATED 0
 #endif

core/src/main/resources/org/teavm/backend/c/heaptrace.c

@@ -2,6 +2,7 @@
 #include "core.h"
 #include "definitions.h"
 #include "memory.h"
+#include "time.h"
 #include <string.h>
 #include <stdint.h>
 #include <inttypes.h>
@@ -9,6 +10,7 @@
 #include <stdlib.h>
 #include <wchar.h>
 #include <wctype.h>
+#include <stdbool.h>
 
 #if TEAVM_WINDOWS
     #include <Windows.h>
@@ -33,6 +35,27 @@ void teavm_outOfMemory() {
 
 static wchar_t* teavm_gc_dumpDirectory = NULL;
 
+#ifdef TEAVM_GC_STATS
+    static int32_t teavm_gc_allocationCount = 0;
+    static int32_t teavm_gc_freeCount = 0;
+    static int32_t teavm_gc_freeByteCount = 0;
+    static int32_t teavm_gc_markCount = 0;
+    static int32_t teavm_gc_dirtyRegionCount = 0;
+    static int32_t teavm_gc_relocatedBlocks = 0;
+    static int32_t teavm_gc_relocatedBytes = 0;
+
+    static int64_t teavm_gc_startTimeMillis;
+    static int64_t teavm_gc_startTime;
+    static int64_t teavm_gc_endTime;
+    static int64_t teavm_gc_markStartTime;
+    static int64_t teavm_gc_markEndTime;
+    static int64_t teavm_gc_sweepStartTime;
+    static int64_t teavm_gc_sweepEndTime;
+    static int64_t teavm_gc_defragStartTime;
+    static int64_t teavm_gc_defragEndTime;
+    static bool teavm_gc_full;
+#endif
+
 #if TEAVM_MEMORY_TRACE
     void teavm_gc_assertSize(int32_t size) {
         if (size % sizeof(void*) != 0) {
@@ -65,6 +88,10 @@ void teavm_gc_allocate(void* address, int32_t size) {
             *map++ = 2;
         }
     #endif
+
+    #if TEAVM_GC_STATS
+        teavm_gc_allocationCount++;
+    #endif
 }
 
 void teavm_gc_free(void* address, int32_t size) {
@@ -86,6 +113,11 @@ void teavm_gc_free(void* address, int32_t size) {
         uint8_t* map = teavm_gc_heapMap + offset;
         memset(map, 0, size);
     #endif
+
+    #if TEAVM_GC_STATS
+        teavm_gc_freeCount++;
+        teavm_gc_freeByteCount += size;
+    #endif
 }
 
 void teavm_gc_assertFree(void* address, int32_t size) {
@@ -106,10 +138,20 @@ void teavm_gc_assertFree(void* address, int32_t size) {
     #endif
 }
 
-void teavm_gc_initMark() {
+void teavm_gc_markStarted() {
     #if TEAVM_MEMORY_TRACE
         memset(teavm_gc_markMap, 0, teavm_gc_availableBytes / sizeof(void*));
     #endif
+
+    #if TEAVM_GC_STATS
+        teavm_gc_markStartTime = teavm_currentTimeNano();
+    #endif
+}
+
+void teavm_gc_markCompleted() {
+    #if TEAVM_GC_STATS
+        teavm_gc_markEndTime = teavm_currentTimeNano();
+    #endif
 }
 
 int32_t teavm_gc_objectSize(void* address) {
@@ -144,7 +186,8 @@ void teavm_gc_mark(void* address) {
         size /= sizeof(void*);
 
         if (*map++ != 1 || *markMap != 0) {
-            fprintf(stderr, "[GC] assertion failed marking object at: %d\n", (int) ((char*) address - (char*) teavm_gc_heapAddress));
+            fprintf(stderr, "[GC] assertion failed marking object at: %d\n",
+                    (int) ((char*) address - (char*) teavm_gc_heapAddress));
             abort();
         }
         *markMap++ = 1;
@@ -156,6 +199,10 @@ void teavm_gc_mark(void* address) {
             *markMap++ = 1;
         }
     #endif
+
+    #if TEAVM_GC_STATS
+        teavm_gc_markCount++;
+    #endif
 }
 
 void teavm_gc_move(void* from, void* to, int32_t size) {
@@ -188,6 +235,11 @@ void teavm_gc_move(void* from, void* to, int32_t size) {
             }
         }
     #endif
+
+    #if TEAVM_GC_STATS
+        teavm_gc_relocatedBlocks++;
+        teavm_gc_relocatedBytes += size;
+    #endif
 }
 
 static FILE* teavm_gc_traceFile = NULL;
@@ -251,8 +303,10 @@ FILE* teavm_gc_openDumpFile(wchar_t* name) {
         #endif
     }
 
-    void teavm_gc_checkHeapConsistency() {
+    void teavm_gc_checkHeapConsistency(bool oldGen, bool offsets) {
+        int32_t lastCheckedRegion = -1;
         TeaVM_Object* obj = teavm_gc_heapAddress;
+        uint16_t* regions = (uint16_t*) teavm_gc_regionsAddress;
         while ((char*) obj < (char*) teavm_gc_heapAddress + teavm_gc_availableBytes) {
             int32_t size;
             if (obj->header == 0) {
@@ -260,6 +314,24 @@ FILE* teavm_gc_openDumpFile(wchar_t* name) {
                 teavm_gc_assertFree(obj, size);
             } else {
                 teavm_verify(obj);
+                if (offsets) {
+                    int64_t offset = (int64_t) ((char*) obj - (char*) teavm_gc_heapAddress);
+                    int32_t objRegion = (int32_t) (offset / teavm_gc_regionSize);
+                    if (objRegion != lastCheckedRegion) {
+                        while (++lastCheckedRegion < objRegion) {
+                            if (regions[lastCheckedRegion] != 0) {
+                                abort();
+                            }
+                        }
+                        int32_t offsetInRegion = (int32_t) (offset % teavm_gc_regionSize);
+                        if (regions[objRegion] != offsetInRegion + 1) {
+                            abort();
+                        }
+                    }
+                }
+                if (oldGen && !(obj->header & 0x40000000)) {
+                    abort();
+                }
                 TeaVM_Class* cls = TEAVM_CLASS_OF(obj);
                 if (cls->itemType != NULL) {
                     if (!(cls->itemType->flags & 2)) {
@@ -297,26 +369,143 @@ FILE* teavm_gc_openDumpFile(wchar_t* name) {
             }
             obj = (TeaVM_Object*) ((char*) obj + size);
         }
+
+        if (offsets) {
+            int32_t lastRegion = (int32_t) (teavm_gc_availableBytes / teavm_gc_regionSize);
+            while (++lastCheckedRegion <= lastRegion) {
+                if (regions[lastCheckedRegion] != 0) {
+                    abort();
+                }
+            }
+        }
     }
 #endif
 
-void teavm_gc_gcStarted() {
+void teavm_gc_gcStarted(int32_t full) {
     #if TEAVM_MEMORY_TRACE
         teavm_writeHeapMemory("start");
-        teavm_gc_checkHeapConsistency();
+        teavm_gc_checkHeapConsistency(false, false);
+    #endif
+
+    #if TEAVM_GC_STATS
+        teavm_gc_startTime = teavm_currentTimeNano();
+        teavm_gc_startTimeMillis = teavm_currentTimeMillis();
+        teavm_gc_full = full;
+    #endif
+}
+
+void teavm_gc_sweepStarted() {
+    #if TEAVM_GC_STATS
+        teavm_gc_sweepStartTime = teavm_currentTimeNano();
     #endif
 }
 
 void teavm_gc_sweepCompleted() {
     #if TEAVM_MEMORY_TRACE
         teavm_writeHeapMemory("sweep");
-        teavm_gc_checkHeapConsistency();
+        teavm_gc_checkHeapConsistency(false, true);
+    #endif
+
+    #if TEAVM_GC_STATS
+        teavm_gc_sweepEndTime = teavm_currentTimeNano();
+    #endif
+}
+
+void teavm_gc_defragStarted() {
+    #if TEAVM_GC_STATS
+        teavm_gc_defragStartTime = teavm_currentTimeNano();
     #endif
 }
 
 void teavm_gc_defragCompleted() {
     #if TEAVM_MEMORY_TRACE
         teavm_writeHeapMemory("defrag");
+        teavm_gc_checkHeapConsistency(true, true);
+    #endif
+
+    #if TEAVM_GC_STATS
+        teavm_gc_defragEndTime = teavm_currentTimeNano();
+    #endif
+}
+
+#define TEAVM_GC_LOG_BUFFER_SIZE 512
+
+#if TEAVM_GC_STATS
+    static void teavm_gc_print(wchar_t* s) {
+        #if TEAVM_WINDOWS_LOG
+            OutputDebugStringW(s);
+        #else
+            fprintf(stderr, "%ls", s);
+        #endif
+    }
+
+    static void teavm_gc_printStats() {
+        wchar_t buffer[TEAVM_GC_LOG_BUFFER_SIZE];
+
+        swprintf(buffer, TEAVM_GC_LOG_BUFFER_SIZE, L"[GC] Garbage collection (%ls) performed at %" PRIu64 ", took %"
+                PRIu64 " ns\n", teavm_gc_full ? L"full" : L"young", teavm_gc_startTimeMillis,
+                 teavm_gc_endTime - teavm_gc_startTime);
+        teavm_gc_print(buffer);
+
+        swprintf(buffer, TEAVM_GC_LOG_BUFFER_SIZE, L"[GC]   Allocations performed before GC: %" PRIu32 "\n",
+                teavm_gc_allocationCount);
+        teavm_gc_print(buffer);
+
+        swprintf(buffer, TEAVM_GC_LOG_BUFFER_SIZE, L"[GC]   Mark phase took %" PRIu64 " ns, %" PRIu32
+                " objects reached\n", teavm_gc_markEndTime - teavm_gc_markStartTime, teavm_gc_markCount);
+        teavm_gc_print(buffer);
+
+        if (!teavm_gc_full) {
+            swprintf(buffer, TEAVM_GC_LOG_BUFFER_SIZE, L"[GC]     Regions scanned from remembered set: %" PRIu32 "\n",
+                    teavm_gc_dirtyRegionCount);
+            teavm_gc_print(buffer);
+        }
+
+        swprintf(buffer, TEAVM_GC_LOG_BUFFER_SIZE, L"[GC]   Sweep phase took %" PRIu64 " ns, %" PRIu32 " regions of %"
+                PRIu32 " bytes freed\n", teavm_gc_sweepEndTime - teavm_gc_sweepStartTime, teavm_gc_freeCount,
+                teavm_gc_freeByteCount);
+        teavm_gc_print(buffer);
+
+        swprintf(buffer, TEAVM_GC_LOG_BUFFER_SIZE, L"[GC]   Defrag phase took %" PRIu64 " ns\n",
+                teavm_gc_defragEndTime - teavm_gc_defragStartTime);
+        teavm_gc_print(buffer);
+
+        swprintf(buffer, TEAVM_GC_LOG_BUFFER_SIZE, L"[GC]     Blocks relocated %" PRId32 " of total %" PRId32 " bytes\n",
+            teavm_gc_relocatedBlocks, teavm_gc_relocatedBytes);
+        teavm_gc_print(buffer);
+    }
+
+    static void teavm_gc_resetStats() {
+        teavm_gc_allocationCount = 0;
+        teavm_gc_markCount = 0;
+        teavm_gc_dirtyRegionCount = 0;
+        teavm_gc_freeCount = 0;
+        teavm_gc_freeByteCount = 0;
+        teavm_gc_relocatedBlocks = 0;
+        teavm_gc_relocatedBytes = 0;
+    }
+#endif
+
+void teavm_gc_gcCompleted() {
+    #if TEAVM_GC_STATS
+        teavm_gc_endTime = teavm_currentTimeNano();
+        teavm_gc_printStats();
+        teavm_gc_resetStats();
+    #endif
+}
+
+void teavm_gc_heapResized(int64_t newSize) {
+    #if TEAVM_GC_STATS
+        wchar_t buffer[TEAVM_GC_LOG_BUFFER_SIZE];
+
+        swprintf(buffer, TEAVM_GC_LOG_BUFFER_SIZE, L"[GC] Heap resized to %" PRIu64 " bytes\n", newSize);
+        teavm_gc_print(buffer);
+    #endif
+}
+
+void teavm_gc_reportDirtyRegion(void* address) {
+    #if TEAVM_GC_STATS
+        teavm_gc_dirtyRegionCount++;
     #endif
 }
 
@@ -329,4 +518,3 @@ void teavm_gc_setDumpDirectory(const wchar_t* path) {
     teavm_gc_dumpDirectory = malloc(bytesLen);
     memcpy(teavm_gc_dumpDirectory, path, bytesLen);
 }
-

core/src/main/resources/org/teavm/backend/c/heaptrace.h

@@ -12,12 +12,18 @@
 extern void teavm_gc_allocate(void* address, int32_t size);
 extern void teavm_gc_free(void* address, int32_t size);
 extern void teavm_gc_assertFree(void* address, int32_t size);
-extern void teavm_gc_initMark();
 extern void teavm_gc_mark(void* address);
 extern void teavm_gc_move(void* from, void* to, int32_t size);
-extern void teavm_gc_gcStarted();
+extern void teavm_gc_gcStarted(int32_t full);
+extern void teavm_gc_markStarted();
+extern void teavm_gc_markCompleted();
+extern void teavm_gc_sweepStarted();
 extern void teavm_gc_sweepCompleted();
+extern void teavm_gc_defragStarted();
 extern void teavm_gc_defragCompleted();
+extern void teavm_gc_gcCompleted();
+extern void teavm_gc_heapResized(int64_t newSize);
+extern void teavm_gc_reportDirtyRegion(void* address);
 extern void teavm_gc_setDumpDirectory(const wchar_t* path);
 extern void teavm_gc_fixHeap();
 extern void teavm_gc_writeHeapDump();

core/src/main/resources/org/teavm/backend/c/memory.c

@@ -1,4 +1,5 @@
 #include "memory.h"
+#include "heaptrace.h"
 #include "definitions.h"
 #include <stdlib.h>
 #include <string.h>
@@ -20,7 +21,7 @@ void* teavm_gc_heapAddress = NULL;
 void* teavm_gc_gcStorageAddress = NULL;
 int32_t teavm_gc_gcStorageSize = INT32_C(0);
 void* teavm_gc_regionsAddress = NULL;
-int32_t teavm_gc_regionSize = INT32_C(32768);
+void* teavm_gc_cardTable = NULL;
 int32_t teavm_gc_regionMaxCount;
 int64_t teavm_gc_availableBytes;
 int64_t teavm_gc_minAvailableBytes;
@@ -110,6 +111,8 @@ void teavm_gc_resizeHeap(int64_t newSize) {
         return;
     }
 
+    teavm_gc_heapResized(newSize);
+
     int32_t workSize = teavm_gc_calculateWorkSize(newSize);
     int32_t regionsSize = teavm_gc_calculateRegionsSize(newSize);
 
@@ -119,6 +122,8 @@ void teavm_gc_resizeHeap(int64_t newSize) {
     int64_t oldWorkSizeAligned = teavm_pageCount(teavm_gc_gcStorageSize);
     int64_t newRegionsSizeAligned = teavm_pageCount(regionsSize * 2);
     int64_t oldRegionsSizeAligned = teavm_pageCount(teavm_gc_regionMaxCount * 2);
+    int64_t newCardTableSizeAligned = teavm_pageCount(regionsSize);
+    int64_t oldCardTableSizeAligned = teavm_pageCount(teavm_gc_regionMaxCount);
 
     if (newSize > teavm_gc_availableBytes) {
         if (newSizeAligned > oldSizeAligned) {
@@ -132,6 +137,10 @@ void teavm_gc_resizeHeap(int64_t newSize) {
             teavm_virtualCommit((char*) teavm_gc_regionsAddress + oldRegionsSizeAligned,
                 newRegionsSizeAligned - oldRegionsSizeAligned);
         }
+        if (newCardTableSizeAligned > oldCardTableSizeAligned) {
+            teavm_virtualCommit((char*) teavm_gc_cardTable + oldCardTableSizeAligned,
+                newCardTableSizeAligned - oldCardTableSizeAligned);
+        }
     } else {
         if (newSizeAligned < oldSizeAligned) {
             teavm_virtualUncommit((char*) teavm_gc_heapAddress + newSizeAligned, oldSizeAligned - newSizeAligned);
@@ -144,6 +153,10 @@ void teavm_gc_resizeHeap(int64_t newSize) {
             teavm_virtualUncommit((char*) teavm_gc_regionsAddress + newRegionsSizeAligned,
                 oldRegionsSizeAligned - newRegionsSizeAligned);
         }
+        if (newCardTableSizeAligned < oldCardTableSizeAligned) {
+            teavm_virtualUncommit((char*) teavm_gc_cardTable + newCardTableSizeAligned,
+                oldCardTableSizeAligned - newCardTableSizeAligned);
+        }
     }
 
     teavm_gc_gcStorageSize = workSize;
@@ -159,6 +172,7 @@ void teavm_initHeap(int64_t minHeap, int64_t maxHeap) {
     teavm_gc_heapAddress = teavm_virtualAlloc(teavm_pageCount(maxHeap));
     teavm_gc_gcStorageAddress = teavm_virtualAlloc(teavm_pageCount(workSize));
     teavm_gc_regionsAddress = teavm_virtualAlloc(teavm_pageCount(regionsSize * 2));
+    teavm_gc_cardTable = teavm_virtualAlloc(teavm_pageCount(regionsSize));
 
     #if TEAVM_MEMORY_TRACE
         int64_t heapMapSize = maxHeap / sizeof(void*);

core/src/main/resources/org/teavm/backend/c/memory.h

@@ -5,7 +5,8 @@ extern void* teavm_gc_heapAddress;
 extern void* teavm_gc_gcStorageAddress;
 extern int32_t teavm_gc_gcStorageSize;
 extern void* teavm_gc_regionsAddress;
-extern int32_t teavm_gc_regionSize;
+extern void* teavm_gc_cardTable;
+#define teavm_gc_regionSize INT32_C(8192)
 extern int32_t teavm_gc_regionMaxCount;
 extern int64_t teavm_gc_availableBytes;
 extern int64_t teavm_gc_minAvailableBytes;

core/src/main/resources/org/teavm/backend/c/references.c

@@ -10,9 +10,11 @@ int32_t teavm_reference_enqueue(TeaVM_Reference* reference) {
     if (queue->last == NULL) {
         queue->first = reference;
     } else {
+        teavm_gc_writeBarrier(queue->last);
         queue->last->next = reference;
     }
     queue->last = reference;
+    teavm_gc_writeBarrier(queue);
 
     return INT32_C(1);
 }
@@ -36,6 +38,7 @@ TeaVM_Reference* teavm_reference_poll(TeaVM_ReferenceQueue* queue) {
 
     TeaVM_Reference* reference = queue->first;
     queue->first = reference->next;
+    teavm_gc_writeBarrier(queue);
     if (queue->first == NULL) {
         queue->last = NULL;
     }

core/src/main/resources/org/teavm/backend/c/stringhash.c

@@ -66,8 +66,8 @@ static void teavm_rehashStrings() {
 }
 
 TeaVM_String* teavm_registerString(TeaVM_String* str) {
-    str->parent.header = TEAVM_PACK_CLASS(teavm_stringClass);
+    str->parent.header = TEAVM_PACK_CLASS(teavm_stringClass) | (int32_t) INT32_C(0x80000000);
-    str->characters->parent.header = TEAVM_PACK_CLASS(teavm_charArrayClass);
+    str->characters->parent.header = TEAVM_PACK_CLASS(teavm_charArrayClass) | (int32_t) INT32_C(0x80000000);
 
     if (teavm_stringHashtable == NULL) {
         teavm_stringHashtableSize = 256;