diff --git a/teavm-core/src/main/java/org/teavm/codegen/MinifyingAliasProvider.java b/teavm-core/src/main/java/org/teavm/codegen/MinifyingAliasProvider.java
index b7eaae831..c79a23ad9 100644
--- a/teavm-core/src/main/java/org/teavm/codegen/MinifyingAliasProvider.java
+++ b/teavm-core/src/main/java/org/teavm/codegen/MinifyingAliasProvider.java
@@ -15,6 +15,7 @@
  */
 package org.teavm.codegen;
 
+import java.util.Arrays;
 import java.util.HashSet;
 import java.util.Set;
 import org.teavm.model.FieldReference;
@@ -26,6 +27,8 @@ import org.teavm.model.MethodReference;
  * @author Alexey Andreev
  */
 public class MinifyingAliasProvider implements AliasProvider {
+    private static Set<String> keywords = new HashSet<>(Arrays.asList("do", "if", "else", "for", "case",
+            "goto", "in", "let", "new", "this", "try", "var", "void", "with"));
     private static String startLetters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
     private static String letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";
     private static String startVirtualLetters = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
@@ -38,7 +41,7 @@ public class MinifyingAliasProvider implements AliasProvider {
         String result;
         do {
             result = getNewAlias(lastVirtual++, startVirtualLetters);
-        } while (!usedAliases.add(result));
+        } while (!usedAliases.add(result) || keywords.contains(result));
         return result;
     }
 
@@ -52,7 +55,7 @@ public class MinifyingAliasProvider implements AliasProvider {
         String result;
         do {
             result = getNewAlias(lastVirtual++, startVirtualLetters);
-        } while (!usedAliases.add(result));
+        } while (!usedAliases.add(result) || keywords.contains(result));
         return result;
     }
 
diff --git a/teavm-core/src/main/java/org/teavm/javascript/Decompiler.java b/teavm-core/src/main/java/org/teavm/javascript/Decompiler.java
index c3948c85e..71349ba54 100644
--- a/teavm-core/src/main/java/org/teavm/javascript/Decompiler.java
+++ b/teavm-core/src/main/java/org/teavm/javascript/Decompiler.java
@@ -249,7 +249,7 @@ public class Decompiler {
         return true;
     }
 
-    public AsyncMethodNode decompileAsyncCacheMiss(MethodHolder method) {
+    private AsyncMethodNode decompileAsyncCacheMiss(MethodHolder method) {
         AsyncMethodNode node = new AsyncMethodNode(method.getReference());
         AsyncProgramSplitter splitter = new AsyncProgramSplitter(classSource, splitMethods);
         splitter.split(method.getProgram());
diff --git a/teavm-core/src/main/java/org/teavm/javascript/Optimizer.java b/teavm-core/src/main/java/org/teavm/javascript/Optimizer.java
index 9ffdd31de..fe0fbf6e7 100644
--- a/teavm-core/src/main/java/org/teavm/javascript/Optimizer.java
+++ b/teavm-core/src/main/java/org/teavm/javascript/Optimizer.java
@@ -15,7 +15,8 @@
  */
 package org.teavm.javascript;
 
-import java.util.*;
+import java.util.BitSet;
+import java.util.List;
 import org.teavm.common.Graph;
 import org.teavm.javascript.ast.AsyncMethodNode;
 import org.teavm.javascript.ast.AsyncMethodPart;
@@ -23,7 +24,11 @@ import org.teavm.javascript.ast.RegularMethodNode;
 import org.teavm.model.Instruction;
 import org.teavm.model.Program;
 import org.teavm.model.Variable;
-import org.teavm.model.util.*;
+import org.teavm.model.util.AsyncProgramSplitter;
+import org.teavm.model.util.DefinitionExtractor;
+import org.teavm.model.util.LivenessAnalyzer;
+import org.teavm.model.util.ProgramUtils;
+import org.teavm.model.util.UsageExtractor;
 
 /**
  *
@@ -59,26 +64,23 @@ public class Optimizer {
         LivenessAnalyzer liveness = new LivenessAnalyzer();
         liveness.analyze(splitter.getOriginalProgram());
 
-        boolean[] preservedVars = new boolean[method.getVariables().size()];
-        int[][] readFrequencies = new int[splitter.size()][];
+        Graph cfg = ProgramUtils.buildControlFlowGraph(splitter.getOriginalProgram());
+
         for (int i = 0; i < splitter.size(); ++i) {
+            boolean[] preservedVars = new boolean[method.getVariables().size()];
             ReadWriteStatsBuilder stats = new ReadWriteStatsBuilder(method.getVariables().size());
             stats.analyze(splitter.getProgram(i));
-            readFrequencies[i] = stats.reads;
             for (int j = 0; j < stats.writes.length; ++j) {
                 if (stats.writes[j] != 1 && stats.reads[j] > 0) {
                     preservedVars[j] = true;
                 }
             }
-        }
 
-        for (int i = 0; i < splitter.size(); ++i) {
-            boolean[] partPreservedVars = preservedVars.clone();
             AsyncMethodPart part = method.getBody().get(i);
             BreakEliminator breakEliminator = new BreakEliminator();
             breakEliminator.eliminate(part.getStatement());
-            findEscapingLiveVars(liveness, splitter, i, partPreservedVars);
-            OptimizingVisitor optimizer = new OptimizingVisitor(partPreservedVars, readFrequencies[i]);
+            findEscapingLiveVars(liveness, cfg, splitter, i, preservedVars);
+            OptimizingVisitor optimizer = new OptimizingVisitor(preservedVars, stats.reads);
             part.getStatement().acceptVisitor(optimizer);
             part.setStatement(optimizer.resultStmt);
         }
@@ -97,38 +99,39 @@ public class Optimizer {
         }
     }
 
-    private void findEscapingLiveVars(LivenessAnalyzer liveness, AsyncProgramSplitter splitter, int partIndex,
-            boolean[] output) {
+    private void findEscapingLiveVars(LivenessAnalyzer liveness, Graph cfg, AsyncProgramSplitter splitter,
+            int partIndex, boolean[] output) {
         Program originalProgram = splitter.getOriginalProgram();
-        Graph cfg = ProgramUtils.buildControlFlowGraph(originalProgram);
+        Program program = splitter.getProgram(partIndex);
         int[] successors = splitter.getBlockSuccessors(partIndex);
         int[] splitPoints = splitter.getSplitPoints(partIndex);
+        int[] originalBlocks = splitter.getOriginalBlocks(partIndex);
 
-        for (int i = 0; i < originalProgram.basicBlockCount(); ++i) {
-            if (successors[i] < 0) {
+        for (int i = 0; i < program.basicBlockCount(); ++i) {
+            if (successors[i] < 0 || originalBlocks[i] < 0) {
                 continue;
             }
 
             // Determine live-out vars
             BitSet liveVars = new BitSet();
-            for (int succ : cfg.outgoingEdges(i)) {
+            for (int succ : cfg.outgoingEdges(originalBlocks[i])) {
                 liveVars.or(liveness.liveIn(succ));
             }
 
             // Remove from live set all variables that are defined in these blocks
             DefinitionExtractor defExtractor = new DefinitionExtractor();
             UsageExtractor useExtractor = new UsageExtractor();
-            List<Instruction> instructions = originalProgram.basicBlockAt(i).getInstructions();
+            List<Instruction> instructions = originalProgram.basicBlockAt(originalBlocks[i]).getInstructions();
             int splitPoint = splitPoints[i];
             for (int j = instructions.size() - 1; j >= splitPoint; --j) {
-                instructions.get(j).acceptVisitor(useExtractor);
                 instructions.get(j).acceptVisitor(defExtractor);
-                for (Variable var : useExtractor.getUsedVariables()) {
-                    liveVars.set(var.getIndex());
-                }
+                instructions.get(j).acceptVisitor(useExtractor);
                 for (Variable var : defExtractor.getDefinedVariables()) {
                     liveVars.clear(var.getIndex());
                 }
+                for (Variable var : useExtractor.getUsedVariables()) {
+                    liveVars.set(var.getIndex());
+                }
             }
 
             // Add live variables to output
diff --git a/teavm-core/src/main/java/org/teavm/model/util/AsyncProgramSplitter.java b/teavm-core/src/main/java/org/teavm/model/util/AsyncProgramSplitter.java
index 2c49e180e..dbfa1ac58 100644
--- a/teavm-core/src/main/java/org/teavm/model/util/AsyncProgramSplitter.java
+++ b/teavm-core/src/main/java/org/teavm/model/util/AsyncProgramSplitter.java
@@ -42,12 +42,8 @@ public class AsyncProgramSplitter {
         this.program = program;
         parts.clear();
         Program initialProgram = createStubCopy(program);
-        Part initialPart = new Part();
+        Part initialPart = new Part(program.basicBlockCount());
         initialPart.program = initialProgram;
-        initialPart.blockSuccessors = new int[program.basicBlockCount()];
-        Arrays.fill(initialPart.blockSuccessors, -1);
-        initialPart.splitPoints = new int[program.basicBlockCount()];
-        Arrays.fill(initialPart.splitPoints, -1);
         parts.add(initialPart);
         partMap.put(0L, 0);
         Step initialStep = new Step();
@@ -63,6 +59,7 @@ public class AsyncProgramSplitter {
                 continue;
             }
             BasicBlock sourceBlock = program.basicBlockAt(step.source);
+            step.targetPart.originalBlocks[step.source] = step.source;
             int last = 0;
             for (int i = 0; i < sourceBlock.getInstructions().size(); ++i) {
                 Instruction insn = sourceBlock.getInstructions().get(i);
@@ -91,7 +88,7 @@ public class AsyncProgramSplitter {
                 }
                 last = i;
 
-                step.targetPart.splitPoints[step.source] = i;
+                step.targetPart.splitPoints[targetBlock.getIndex()] = i;
 
                 // If this instruction already separates program, end with current block and refer to the
                 // existing part
@@ -103,14 +100,10 @@ public class AsyncProgramSplitter {
 
                 // Create a new part
                 Program nextProgram = createStubCopy(program);
-                Part part = new Part();
+                Part part = new Part(program.basicBlockCount() + 1);
                 part.program = nextProgram;
                 int partId = parts.size();
                 parts.add(part);
-                part.blockSuccessors = new int[program.basicBlockCount() + 1];
-                Arrays.fill(part.blockSuccessors, -1);
-                part.splitPoints = new int[program.basicBlockCount() + 1];
-                Arrays.fill(part.splitPoints, -1);
 
                 // Mark current instruction as a separator and remember which part is in charge.
                 partMap.put(key, partId);
@@ -126,6 +119,7 @@ public class AsyncProgramSplitter {
                             nextProgram));
                 }
                 step.targetPart = part;
+                part.originalBlocks[targetBlock.getIndex()] = step.source;
             }
             targetBlock.getInstructions().addAll(ProgramUtils.copyInstructions(sourceBlock,
                     last, sourceBlock.getInstructions().size(), targetBlock.getProgram()));
@@ -153,8 +147,10 @@ public class AsyncProgramSplitter {
 
         for (Part part : parts) {
             IntegerArray blockSuccessors = IntegerArray.of(part.blockSuccessors);
+            IntegerArray originalBlocks = IntegerArray.of(part.originalBlocks);
+            IntegerArray splitPoints = IntegerArray.of(part.splitPoints);
             AsyncProgramSplittingBackend splittingBackend = new AsyncProgramSplittingBackend(
-                    new ProgramNodeSplittingBackend(part.program), blockSuccessors);
+                    new ProgramNodeSplittingBackend(part.program), blockSuccessors, originalBlocks, splitPoints);
             Graph graph = ProgramUtils.buildControlFlowGraphWithTryCatch(part.program);
             int[] weights = new int[graph.size()];
             for (int i = 0; i < part.program.basicBlockCount(); ++i) {
@@ -162,6 +158,8 @@ public class AsyncProgramSplitter {
             }
             GraphUtils.splitIrreducibleGraph(graph, weights, splittingBackend);
             part.blockSuccessors = splittingBackend.blockSuccessors.getAll();
+            part.originalBlocks = splittingBackend.originalBlocks.getAll();
+            part.splitPoints = splittingBackend.splitPoints.getAll();
         }
         partMap.clear();
     }
@@ -221,10 +219,24 @@ public class AsyncProgramSplitter {
         return parts.get(index).splitPoints.clone();
     }
 
-    private static class Part {
+    public int[] getOriginalBlocks(int index) {
+        return parts.get(index).originalBlocks.clone();
+    }
+
+    static class Part {
         Program program;
         int[] blockSuccessors;
         int[] splitPoints;
+        int[] originalBlocks;
+
+        public Part(int blockCount) {
+            blockSuccessors = new int[blockCount];
+            Arrays.fill(blockSuccessors, -1);
+            splitPoints = new int[blockCount];
+            Arrays.fill(splitPoints, -1);
+            originalBlocks = new int[blockCount];
+            Arrays.fill(originalBlocks, -1);
+        }
     }
 
     private static class Step {
@@ -235,10 +247,15 @@ public class AsyncProgramSplitter {
     private static class AsyncProgramSplittingBackend implements GraphSplittingBackend {
         private GraphSplittingBackend inner;
         private IntegerArray blockSuccessors;
+        private IntegerArray originalBlocks;
+        private IntegerArray splitPoints;
 
-        public AsyncProgramSplittingBackend(GraphSplittingBackend inner, IntegerArray blockSuccessors) {
+        public AsyncProgramSplittingBackend(GraphSplittingBackend inner, IntegerArray blockSuccessors,
+                IntegerArray originalBlocks, IntegerArray splitPoints) {
             this.inner = inner;
             this.blockSuccessors = blockSuccessors;
+            this.originalBlocks = originalBlocks;
+            this.splitPoints = splitPoints;
         }
 
         @Override
@@ -249,8 +266,12 @@ public class AsyncProgramSplitter {
                 int node = nodes[i];
                 if (blockSuccessors.size() <= copy) {
                     blockSuccessors.add(-1);
+                    splitPoints.add(-1);
+                    originalBlocks.add(-1);
                 }
                 blockSuccessors.set(copy, blockSuccessors.get(node));
+                originalBlocks.set(copy, originalBlocks.get(node));
+                splitPoints.set(copy, splitPoints.get(node));
             }
             return copies;
         }
diff --git a/teavm-core/src/main/java/org/teavm/model/util/RegisterAllocator.java b/teavm-core/src/main/java/org/teavm/model/util/RegisterAllocator.java
index 8908915fa..9cf08eb82 100644
--- a/teavm-core/src/main/java/org/teavm/model/util/RegisterAllocator.java
+++ b/teavm-core/src/main/java/org/teavm/model/util/RegisterAllocator.java
@@ -60,6 +60,10 @@ public class RegisterAllocator {
         for (int i = 0; i < colors.length; ++i) {
             program.variableAt(i).setRegister(colors[i]);
         }
+
+        for (int i = 0; i < program.basicBlockCount(); ++i) {
+            program.basicBlockAt(i).getPhis().clear();
+        }
     }
 
     private int[] getVariableCategories(ProgramReader program, MethodReference method) {