diff --git a/core/src/main/java/org/teavm/model/lowlevel/ExceptionHandlingShadowStackContributor.java b/core/src/main/java/org/teavm/model/lowlevel/ExceptionHandlingShadowStackContributor.java
index ac2ab29de..4ebe03a3c 100644
--- a/core/src/main/java/org/teavm/model/lowlevel/ExceptionHandlingShadowStackContributor.java
+++ b/core/src/main/java/org/teavm/model/lowlevel/ExceptionHandlingShadowStackContributor.java
@@ -191,6 +191,17 @@ public class ExceptionHandlingShadowStackContributor {
         BasicBlock initialBlock = block;
 
         for (Instruction insn : block) {
+            insn.acceptVisitor(defExtractor);
+            for (Variable definedVar : defExtractor.getDefinedVariables()) {
+                for (TryCatchBlock tryCatch : block.getTryCatchBlocks()) {
+                    int jointReceiver = jointReceiverMaps.get(tryCatch.getHandler().getIndex())[definedVar.getIndex()];
+                    if (jointReceiver >= 0) {
+                        currentJointSources[jointReceiver] = definedVar.getIndex();
+                    }
+                }
+                variablesDefinedHere.add(definedVar.getIndex());
+            }
+
             if (isCallInstruction(insn)) {
                 BasicBlock next;
                 boolean last = false;
@@ -250,17 +261,6 @@ public class ExceptionHandlingShadowStackContributor {
                 block = next;
                 variablesDefinedHere.clear();
             }
-
-            insn.acceptVisitor(defExtractor);
-            for (Variable definedVar : defExtractor.getDefinedVariables()) {
-                for (TryCatchBlock tryCatch : block.getTryCatchBlocks()) {
-                    int jointReceiver = jointReceiverMaps.get(tryCatch.getHandler().getIndex())[definedVar.getIndex()];
-                    if (jointReceiver >= 0) {
-                        currentJointSources[jointReceiver] = definedVar.getIndex();
-                    }
-                }
-                variablesDefinedHere.add(definedVar.getIndex());
-            }
         }
 
         fixOutgoingPhis(initialBlock, block, currentJointSources, variablesDefinedHere);
diff --git a/core/src/main/java/org/teavm/model/lowlevel/NullCheckInsertion.java b/core/src/main/java/org/teavm/model/lowlevel/NullCheckInsertion.java
index 920247f62..4c8d1d5a0 100644
--- a/core/src/main/java/org/teavm/model/lowlevel/NullCheckInsertion.java
+++ b/core/src/main/java/org/teavm/model/lowlevel/NullCheckInsertion.java
@@ -15,6 +15,8 @@
  */
 package org.teavm.model.lowlevel;
 
+import com.carrotsearch.hppc.IntHashSet;
+import com.carrotsearch.hppc.IntSet;
 import java.util.function.BiConsumer;
 import java.util.function.Function;
 import org.teavm.model.BasicBlock;
@@ -32,6 +34,8 @@ import org.teavm.model.instructions.NullCheckInstruction;
 import org.teavm.model.instructions.PutFieldInstruction;
 import org.teavm.model.instructions.RaiseInstruction;
 import org.teavm.model.instructions.UnwrapArrayInstruction;
+import org.teavm.model.util.DominatorWalker;
+import org.teavm.model.util.DominatorWalkerCallback;
 import org.teavm.model.util.PhiUpdater;
 
 public class NullCheckInsertion {
@@ -42,23 +46,51 @@ public class NullCheckInsertion {
     }
 
     public void transformProgram(Program program, MethodReference methodReference) {
-        if (!characteristics.isManaged(methodReference)) {
+        if (!characteristics.isManaged(methodReference) || program.basicBlockCount() == 0) {
             return;
         }
 
-        InsertionVisitor visitor = new InsertionVisitor();
-        for (BasicBlock block : program.getBasicBlocks()) {
-            for (Instruction instruction : block) {
-                instruction.acceptVisitor(visitor);
-            }
-        }
+        InsertionVisitor visitor = new InsertionVisitor(program.variableCount());
+        new DominatorWalker(program).walk(visitor);
         if (visitor.changed) {
             new PhiUpdater().updatePhis(program, methodReference.parameterCount() + 1);
         }
     }
 
-    class InsertionVisitor extends AbstractInstructionVisitor {
+    class InsertionVisitor extends AbstractInstructionVisitor implements DominatorWalkerCallback<BlockNullness> {
         boolean changed;
+        boolean[] notNullVariables;
+        BlockNullness blockNullness;
+
+        InsertionVisitor(int variableCount) {
+            notNullVariables = new boolean[variableCount];
+            if (variableCount > 0) {
+                notNullVariables[0] = true;
+            }
+        }
+
+        @Override
+        public BlockNullness visit(BasicBlock block) {
+            blockNullness = new BlockNullness();
+
+            if (block.getExceptionVariable() != null) {
+                notNullVariables[block.getExceptionVariable().getIndex()] = true;
+                blockNullness.notNullVariables.add(block.getExceptionVariable().getIndex());
+            }
+
+            for (Instruction instruction : block) {
+                instruction.acceptVisitor(this);
+            }
+
+            return blockNullness;
+        }
+
+        @Override
+        public void endVisit(BasicBlock block, BlockNullness state) {
+            for (int variable : state.notNullVariables.toArray()) {
+                notNullVariables[variable] = false;
+            }
+        }
 
         @Override
         public void visit(RaiseInstruction insn) {
@@ -114,6 +146,13 @@ public class NullCheckInsertion {
                 return;
             }
 
+            if (notNullVariables[value.getIndex()]) {
+                return;
+            }
+
+            notNullVariables[value.getIndex()] = true;
+            blockNullness.notNullVariables.add(value.getIndex());
+
             NullCheckInstruction nullCheck = new NullCheckInstruction();
             nullCheck.setValue(value);
             nullCheck.setReceiver(value);
@@ -123,4 +162,8 @@ public class NullCheckInsertion {
             changed = true;
         }
     }
+
+    static class BlockNullness {
+        IntSet notNullVariables = new IntHashSet();
+    }
 }
diff --git a/core/src/main/java/org/teavm/model/util/LivenessAnalyzer.java b/core/src/main/java/org/teavm/model/util/LivenessAnalyzer.java
index ec86ceaea..7089161e9 100644
--- a/core/src/main/java/org/teavm/model/util/LivenessAnalyzer.java
+++ b/core/src/main/java/org/teavm/model/util/LivenessAnalyzer.java
@@ -48,8 +48,8 @@ public class LivenessAnalyzer {
     public void analyze(Program program) {
         Graph cfg = ProgramUtils.buildControlFlowGraph(program);
         DominatorTree dominatorTree = GraphUtils.buildDominatorTree(cfg);
-        liveVars = new BitSet[cfg.size()];
-        liveOutVars = new BitSet[cfg.size()];
+        liveVars = new BitSet[program.basicBlockCount()];
+        liveOutVars = new BitSet[program.basicBlockCount()];
         for (int i = 0; i < liveVars.length; ++i) {
             liveVars[i] = new BitSet(program.basicBlockCount());
             liveOutVars[i] = new BitSet(program.basicBlockCount());
diff --git a/core/src/main/java/org/teavm/vm/TeaVM.java b/core/src/main/java/org/teavm/vm/TeaVM.java
index afad5a10a..c15692533 100644
--- a/core/src/main/java/org/teavm/vm/TeaVM.java
+++ b/core/src/main/java/org/teavm/vm/TeaVM.java
@@ -760,8 +760,8 @@ public class TeaVM implements TeaVMHost, ServiceRepository {
             optimizations.add(new LoopInvariantMotion());
         }
         optimizations.add(new GlobalValueNumbering(optimizationLevel == TeaVMOptimizationLevel.SIMPLE));
+        optimizations.add(new RedundantNullCheckElimination());
         if (optimizationLevel.ordinal() >= TeaVMOptimizationLevel.ADVANCED.ordinal()) {
-            optimizations.add(new RedundantNullCheckElimination());
             optimizations.add(new ConstantConditionElimination());
             optimizations.add(new RedundantJumpElimination());
             optimizations.add(new UnusedVariableElimination());
diff --git a/platform/src/main/java/org/teavm/platform/plugin/AsyncMethodProcessor.java b/platform/src/main/java/org/teavm/platform/plugin/AsyncMethodProcessor.java
index fbf906e28..71eb68fa8 100644
--- a/platform/src/main/java/org/teavm/platform/plugin/AsyncMethodProcessor.java
+++ b/platform/src/main/java/org/teavm/platform/plugin/AsyncMethodProcessor.java
@@ -39,6 +39,7 @@ import org.teavm.model.instructions.ConstructInstruction;
 import org.teavm.model.instructions.ExitInstruction;
 import org.teavm.model.instructions.InvocationType;
 import org.teavm.model.instructions.InvokeInstruction;
+import org.teavm.model.instructions.JumpInstruction;
 import org.teavm.runtime.Fiber;
 
 public class AsyncMethodProcessor implements ClassHolderTransformer {
@@ -89,8 +90,14 @@ public class AsyncMethodProcessor implements ClassHolderTransformer {
 
         Program program = new Program();
         method.setProgram(program);
+
+        BasicBlock startBlock = program.createBasicBlock();
         BasicBlock block = program.createBasicBlock();
 
+        JumpInstruction jumpToBlock = new JumpInstruction();
+        jumpToBlock.setTarget(block);
+        startBlock.add(jumpToBlock);
+
         InvokeInstruction constructorInvocation = new InvokeInstruction();
         constructorInvocation.setType(InvocationType.SPECIAL);
         List<ValueType> signature = new ArrayList<>();