diff --git a/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java b/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java
index 0d577d2..4eb3bf3 100644
--- a/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java
+++ b/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java
@@ -41,6 +41,7 @@ public CompiledFunction(Symbol.FunctionTypeSymbol functionSymbol, TypeDictionary
         AST.FuncDecl funcDecl = (AST.FuncDecl) functionSymbol.functionDecl;
         this.functionType = (Type.TypeFunction) functionSymbol.type;
         this.registerPool = new RegisterPool();
+        // Incremental SSA is an optional feature
         this.issa = (options != null && options.contains(Options.ISSA)) ? new IncrementalSSABraun(this) : new NoopIncrementalSSA();
         setVirtualRegisters(funcDecl.scope);
         this.BID = 0;
@@ -49,6 +50,7 @@ public CompiledFunction(Symbol.FunctionTypeSymbol functionSymbol, TypeDictionary
         this.currentBreakTarget = null;
         this.currentContinueTarget = null;
         this.typeDictionary = typeDictionary;
+        issa.sealBlock(entry);          // Incremental SSA is an optional feature
         generateArgInstructions(funcDecl.scope);
         compileStatement(funcDecl.block);
         exitBlockIfNeeded();
@@ -135,7 +137,7 @@ else if (virtualStack.size() > 1)
 
     public void code(Instruction instruction) {
         currentBlock.add(instruction);
-        instruction.block = currentBlock;
+        assert instruction.block == currentBlock;
     }
 
     private void compileStatement(AST.Stmt statement) {
@@ -225,12 +227,12 @@ private void compileWhile(AST.WhileStmt whileStmt) {
             codeIndexedLoad();
         codeCBR(currentBlock, pop(), bodyBlock, exitBlock);
         assert vstackEmpty();
-        startSealedBlock(bodyBlock);  // ISSA If we seal this here fib test fails, wrong code generated, why?
+        startSealedBlock(bodyBlock);  // ISSA Body is immediately sealed as no new predecessors possible
         compileStatement(whileStmt.stmt);
         if (!isBlockTerminated(currentBlock))
             jumpTo(loopHead);
         issa.sealBlock(loopHead);
-        startSealedBlock(exitBlock);
+        startSealedBlock(exitBlock);    // ISSA seal exit block (breaks already done)
         currentContinueTarget = savedContinueTarget;
         currentBreakTarget = savedBreakTarget;
     }
@@ -450,7 +452,7 @@ private boolean codeBoolean(AST.BinaryExpr binaryExpr) {
         }
         startSealedBlock(l1);       // ISSA seal immediately
         compileExpr(binaryExpr.expr2);
-        var temp = ensureTemp();
+        var temp = ensureTemp();    // Normally temps are SSA but this temp gets two assignments, thus must be included during SSA conversion
         jumpTo(l3);
         startSealedBlock(l2);       // ISSA seal immediately
         // Below we must write to the same temp
@@ -464,7 +466,7 @@ private boolean codeBoolean(AST.BinaryExpr binaryExpr) {
     private boolean compileBinaryExpr(AST.BinaryExpr binaryExpr) {
         String opCode = binaryExpr.op.str;
         if (opCode.equals("&&") ||
-                opCode.equals("||")) {
+            opCode.equals("||")) {
             return codeBoolean(binaryExpr);
         }
         boolean indexed = compileExpr(binaryExpr.expr1);
@@ -476,7 +478,7 @@ private boolean compileBinaryExpr(AST.BinaryExpr binaryExpr) {
         Operand right = pop();
         Operand left = pop();
         if (left instanceof Operand.NullConstantOperand &&
-                right instanceof Operand.NullConstantOperand) {
+            right instanceof Operand.NullConstantOperand) {
             long value = 0;
             switch (opCode) {
                 case "==": value = 1; break;
@@ -602,15 +604,17 @@ private Operand top() {
         return virtualStack.getLast();
     }
 
+    private boolean vstackEmpty() {
+        return virtualStack.isEmpty();
+    }
+
     private Operand.TempRegisterOperand codeIndexedLoad() {
         Operand indexed = pop();
         var temp = createTemp(indexed.type);
-        if (indexed instanceof Operand.LoadIndexedOperand loadIndexedOperand) {
+        if (indexed instanceof Operand.LoadIndexedOperand loadIndexedOperand)
             codeArrayLoad(loadIndexedOperand, temp);
-        }
-        else if (indexed instanceof Operand.LoadFieldOperand loadFieldOperand) {
+        else if (indexed instanceof Operand.LoadFieldOperand loadFieldOperand)
             codeGetField(loadFieldOperand, temp);
-        }
         else
             codeMove(indexed, temp);
         return temp;
@@ -619,12 +623,10 @@ else if (indexed instanceof Operand.LoadFieldOperand loadFieldOperand) {
     private void codeIndexedStore() {
         Operand value = pop();
         Operand indexed = pop();
-        if (indexed instanceof Operand.LoadIndexedOperand loadIndexedOperand) {
+        if (indexed instanceof Operand.LoadIndexedOperand loadIndexedOperand)
             codeArrayStore(value, loadIndexedOperand);
-        }
-        else if (indexed instanceof Operand.LoadFieldOperand loadFieldOperand) {
+        else if (indexed instanceof Operand.LoadFieldOperand loadFieldOperand)
             codeSetField(value, loadFieldOperand);
-        }
         else
             codeMove(value, indexed);
     }
@@ -638,6 +640,15 @@ else if (type instanceof Type.TypeStruct typeStruct)
             throw new CompilerException("Unexpected type: " + type);
     }
 
+    private void codeStoreAppend() {
+        var operand = issa.read(pop());
+        Operand.RegisterOperand arrayOperand = (Operand.RegisterOperand) issa.read(top());
+        var insn = new Instruction.AStoreAppend(arrayOperand, operand);
+        issa.recordUse(arrayOperand, insn);
+        issa.recordUse(operand, insn);
+        code(insn);
+    }
+
     private void codeNewArray(Type.TypeArray typeArray) {
         var temp = createTemp(typeArray);
         var target = (Operand.RegisterOperand) issa.write(temp);
@@ -654,15 +665,6 @@ private void codeNewStruct(Type.TypeStruct typeStruct) {
         code(insn);
     }
 
-    private void codeStoreAppend() {
-        var operand = issa.read(pop());
-        Operand.RegisterOperand arrayOperand = (Operand.RegisterOperand) issa.read(top());
-        var insn = new Instruction.AStoreAppend(arrayOperand, operand);
-        issa.recordUse(arrayOperand, insn);
-        issa.recordUse(operand, insn);
-        code(insn);
-    }
-
     private void codeArg(Operand.LocalRegisterOperand target) {
         var newtarget = (Operand.RegisterOperand) issa.write(target);
         var insn = new Instruction.ArgInstruction(newtarget);
@@ -774,10 +776,6 @@ private void codeSetField(Operand value, Operand.LoadFieldOperand loadFieldOpera
         code(insn);
     }
 
-    private boolean vstackEmpty() {
-        return virtualStack.isEmpty();
-    }
-
     public StringBuilder toStr(StringBuilder sb, boolean verbose) {
         if (verbose) {
             sb.append(this.functionType.describe()).append("\n");
diff --git a/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/EnterSSA.java b/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/EnterSSA.java
index 13a8556..fc1d275 100644
--- a/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/EnterSSA.java
+++ b/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/EnterSSA.java
@@ -94,6 +94,8 @@ void insertPhis() {
                 while (b != null) {
                     visited.set(b.bid);
                     for (BasicBlock d: b.dominationFrontier) {
+                        if (d == function.exit) // The exit block does not need any phis as it has no instructions
+                            continue;
                         // insert phi for x in d
                         d.insertPhiFor(x);
                         if (!visited.get(d.bid))
diff --git a/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/Options.java b/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/Options.java
index b49d9b5..e71988c 100644
--- a/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/Options.java
+++ b/optvm/src/main/java/com/compilerprogramming/ezlang/compiler/Options.java
@@ -23,6 +23,7 @@ public enum Options {
 
     public static final EnumSet<Options> NONE = EnumSet.noneOf(Options.class);
     public static final EnumSet<Options> OPT = EnumSet.of(Options.OPTIMIZE,Options.SCCP,Options.CCP,Options.REGALLOC);
+    public static final EnumSet<Options> OPT_ISSA = EnumSet.of(Options.OPTIMIZE,Options.ISSA,Options.SCCP,Options.CCP,Options.REGALLOC);
     public static final EnumSet<Options> VERBOSE = EnumSet.range(DUMP_INITIAL_IR, DUMP_POST_CHAITIN_IR);
     public static final EnumSet<Options> OPT_VERBOSE = EnumSet.range(OPTIMIZE, DUMP_POST_CHAITIN_IR);
 }
diff --git a/optvm/src/test/java/com/compilerprogramming/ezlang/compiler/TestIncrementalSSA.java b/optvm/src/test/java/com/compilerprogramming/ezlang/compiler/TestIncrementalSSA.java
index 864cb42..546425d 100644
--- a/optvm/src/test/java/com/compilerprogramming/ezlang/compiler/TestIncrementalSSA.java
+++ b/optvm/src/test/java/com/compilerprogramming/ezlang/compiler/TestIncrementalSSA.java
@@ -1,5 +1,6 @@
 package com.compilerprogramming.ezlang.compiler;
 
+import org.junit.Assert;
 import org.junit.Test;
 
 import java.util.EnumSet;
@@ -7,8 +8,8 @@
 public class TestIncrementalSSA {
     String compileSrc(String src) {
         var compiler = new Compiler();
-        var typeDict = compiler.compileSrc(src, EnumSet.of(Options.ISSA,Options.DUMP_SSA_IR));
-        return compiler.dumpIR(typeDict,true);
+        var typeDict = compiler.compileSrc(src, EnumSet.of(Options.ISSA));
+        return compiler.dumpIR(typeDict, true);
     }
 
     @Test
@@ -23,7 +24,30 @@ func foo(d: Int) {
                 }
                 """;
         String result = compileSrc(src);
-        System.out.println(result);
+        Assert.assertEquals("""
+                func foo(d: Int)
+                Reg #0 d 0
+                Reg #1 a 1
+                Reg #2 b 2
+                Reg #3 c 3
+                Reg #4 %t4 4
+                Reg #5 %t5 5
+                Reg #6 a_1 1
+                Reg #7 %t7 7
+                Reg #8 c_1 3
+                L0:
+                    arg d
+                    a = 42
+                    b = a
+                    %t4 = a+b
+                    c = %t4
+                    %t5 = c+23
+                    a_1 = %t5
+                    %t7 = a_1+d
+                    c_1 = %t7
+                    goto  L1
+                L1:
+                """, result);
     }
 
     @Test
@@ -43,7 +67,33 @@ func foo(d: Int)->Int {
                 }
                 """;
         String result = compileSrc(src);
-        System.out.println(result);
+        Assert.assertEquals("""
+                func foo(d: Int)->Int
+                Reg #0 d 0
+                Reg #1 a 1
+                Reg #2 %t2 2
+                Reg #3 a_1 1
+                Reg #4 %t4 4
+                Reg #5 a_2 1
+                Reg #6 a_3 1
+                L0:
+                    arg d
+                    a = 42
+                    if d goto L2 else goto L3
+                L2:
+                    %t2 = a+1
+                    a_1 = %t2
+                    goto  L4
+                L4:
+                    a_3 = phi(a_1, a_2)
+                    ret a_3
+                    goto  L1
+                L1:
+                L3:
+                    %t4 = a-1
+                    a_2 = %t4
+                    goto  L4
+                """, result);
     }
 
     @Test
@@ -60,7 +110,37 @@ func factorial(num: Int)->Int {
                 }
                 """;
         String result = compileSrc(src);
-        System.out.println(result);
+        Assert.assertEquals("""
+                func factorial(num: Int)->Int
+                Reg #0 num 0
+                Reg #1 result 1
+                Reg #2 %t2 2
+                Reg #3 num_1 0
+                Reg #4 %t4 4
+                Reg #5 result_1 1
+                Reg #6 result_2 1
+                Reg #7 %t7 7
+                Reg #8 num_2 0
+                L0:
+                    arg num
+                    result = 1
+                    goto  L2
+                L2:
+                    result_1 = phi(result, result_2)
+                    num_1 = phi(num, num_2)
+                    %t2 = num_1>1
+                    if %t2 goto L3 else goto L4
+                L3:
+                    %t4 = result_1*num_1
+                    result_2 = %t4
+                    %t7 = num_1-1
+                    num_2 = %t7
+                    goto  L2
+                L4:
+                    ret result_1
+                    goto  L1
+                L1:
+                """, result);
     }
 
 
@@ -102,7 +182,189 @@ func example14_66(p: Int, q: Int, r: Int, s: Int, t: Int) {
                 }
                 """;
         String result = compileSrc(src);
-        System.out.println(result);
+        Assert.assertEquals("""
+                func print(a: Int,b: Int,c: Int,d: Int)
+                Reg #0 a 0
+                Reg #1 b 1
+                Reg #2 c 2
+                Reg #3 d 3
+                L0:
+                    arg a
+                    arg b
+                    arg c
+                    arg d
+                    goto  L1
+                L1:
+                func example14_66(p: Int,q: Int,r: Int,s: Int,t: Int)
+                Reg #0 p 0
+                Reg #1 q 1
+                Reg #2 r 2
+                Reg #3 s 3
+                Reg #4 t 4
+                Reg #5 i 5
+                Reg #6 j 6
+                Reg #7 k 7
+                Reg #8 l 8
+                Reg #9 p_1 0
+                Reg #10 i_1 5
+                Reg #11 j_1 6
+                Reg #12 q_1 1
+                Reg #13 l_1 8
+                Reg #14 l_2 8
+                Reg #15 %t15 15
+                Reg #16 k_1 7
+                Reg #17 k_2 7
+                Reg #18 k_3 7
+                Reg #19 %t19 19
+                Reg #20 k_4 7
+                Reg #21 %t21 21
+                Reg #22 i_2 5
+                Reg #23 i_3 5
+                Reg #24 %t24 24
+                Reg #25 j_2 6
+                Reg #26 j_3 6
+                Reg #27 j_4 6
+                Reg #28 %t28 28
+                Reg #29 k_5 7
+                Reg #30 %t30 30
+                Reg #31 l_3 8
+                Reg #32 l_4 8
+                Reg #33 l_5 8
+                Reg #34 r_1 2
+                Reg #35 %t35 35
+                Reg #36 l_6 8
+                Reg #37 l_7 8
+                Reg #38 %t38 38
+                Reg #39 s_1 3
+                Reg #40 s_2 3
+                Reg #41 r_2 2
+                Reg #42 r_3 2
+                Reg #43 r_4 2
+                Reg #44 r_5 2
+                Reg #45 s_3 3
+                Reg #46 s_4 3
+                Reg #47 s_5 3
+                Reg #48 l_8 8
+                Reg #49 %t49 49
+                Reg #50 i_4 5
+                Reg #51 i_5 5
+                Reg #52 i_6 5
+                Reg #53 i_7 5
+                Reg #54 %t54 54
+                Reg #55 t_1 4
+                Reg #56 t_2 4
+                Reg #57 t_3 4
+                Reg #58 t_4 4
+                Reg #59 t_5 4
+                Reg #60 t_6 4
+                Reg #61 p_2 0
+                Reg #62 p_3 0
+                Reg #63 p_4 0
+                Reg #64 p_5 0
+                Reg #65 p_6 0
+                Reg #66 q_2 1
+                Reg #67 q_3 1
+                Reg #68 q_4 1
+                Reg #69 q_5 1
+                Reg #70 q_6 1
+                Reg #71 r_6 2
+                Reg #72 s_6 3
+                Reg #73 j_5 6
+                Reg #74 j_6 6
+                Reg #75 j_7 6
+                Reg #76 k_6 7
+                Reg #77 k_7 7
+                Reg #78 k_8 7
+                Reg #79 l_9 8
+                L0:
+                    arg p
+                    arg q
+                    arg r
+                    arg s
+                    arg t
+                    i = 1
+                    j = 1
+                    k = 1
+                    l = 1
+                    goto  L2
+                L2:
+                    t_5 = phi(t, t_1)
+                    s_5 = phi(s, s_2)
+                    r_4 = phi(r, r_1)
+                    l_5 = phi(l, l_9)
+                    j_4 = phi(j, j_5)
+                    k_2 = phi(k, k_6)
+                    q_1 = phi(q, q_2)
+                    i_1 = phi(i, i_7)
+                    p_1 = phi(p, p_2)
+                    if 1 goto L3 else goto L4
+                L3:
+                    if p_1 goto L5 else goto L6
+                L5:
+                    j_1 = i_1
+                    if q_1 goto L8 else goto L9
+                L8:
+                    l_1 = 2
+                    goto  L10
+                L10:
+                    l_4 = phi(l_1, l_2)
+                    %t15 = k_2+1
+                    k_3 = %t15
+                    goto  L7
+                L7:
+                    l_3 = phi(l_4, l_5)
+                    k_5 = phi(k_3, k_4)
+                    j_2 = phi(j_1, j_4)
+                    %t21 = i_1
+                    %t24 = j_2
+                    %t28 = k_5
+                    %t30 = l_3
+                    call print params %t21, %t24, %t28, %t30
+                    goto  L11
+                L11:
+                    l_6 = phi(l_3, l_8)
+                    if 1 goto L12 else goto L13
+                L12:
+                    if r_4 goto L14 else goto L15
+                L14:
+                    %t35 = l_6+4
+                    l_7 = %t35
+                    goto  L15
+                L15:
+                    l_8 = phi(l_6, l_7)
+                    %t38 = !s_5
+                    if %t38 goto L16 else goto L17
+                L16:
+                    goto  L13
+                L13:
+                    l_9 = phi(l_6, l_8)
+                    k_6 = phi(k_5, k_7)
+                    j_5 = phi(j_2, j_6)
+                    q_2 = phi(q_1, q_3)
+                    p_2 = phi(p_1, p_3)
+                    t_1 = phi(t_5, t_2)
+                    i_4 = phi(i_1, i_5)
+                    %t49 = i_4+6
+                    i_7 = %t49
+                    %t54 = !t_1
+                    if %t54 goto L18 else goto L19
+                L18:
+                    goto  L4
+                L4:
+                    goto  L1
+                L1:
+                L19:
+                    goto  L2
+                L17:
+                    goto  L11
+                L9:
+                    l_2 = 3
+                    goto  L10
+                L6:
+                    %t19 = k_2+2
+                    k_4 = %t19
+                    goto  L7
+                """, result);
     }
 
     @Test
@@ -127,6 +389,136 @@ func foo()->Int {
                 }
                 """;
         String result = compileSrc(src);
+        Assert.assertEquals("""
+                func fib(n: Int)->Int
+                Reg #0 n 0
+                Reg #1 i 1
+                Reg #2 temp 2
+                Reg #3 f1 3
+                Reg #4 f2 4
+                Reg #5 %t5 5
+                Reg #6 i_1 1
+                Reg #7 %t7 7
+                Reg #8 f1_1 3
+                Reg #9 f2_1 4
+                Reg #10 f1_2 3
+                Reg #11 f2_2 4
+                Reg #12 %t12 12
+                Reg #13 i_2 1
+                L0:
+                    arg n
+                    f1 = 1
+                    f2 = 1
+                    i = n
+                    goto  L2
+                L2:
+                    f2_1 = phi(f2, f2_2)
+                    f1_1 = phi(f1, f1_2)
+                    i_1 = phi(i, i_2)
+                    %t5 = i_1>1
+                    if %t5 goto L3 else goto L4
+                L3:
+                    %t7 = f1_1+f2_1
+                    temp = %t7
+                    f1_2 = f2_1
+                    f2_2 = temp
+                    %t12 = i_1-1
+                    i_2 = %t12
+                    goto  L2
+                L4:
+                    ret f2_1
+                    goto  L1
+                L1:
+                func foo()->Int
+                Reg #0 %t0 0
+                Reg #1 %t1 1
+                L0:
+                    %t0 = 10
+                    %t1 = call fib params %t0
+                    ret %t1
+                    goto  L1
+                L1:
+                """, result);
         System.out.println(result);
     }
+
+    // http://users.csc.calpoly.edu/~akeen/courses/csc431/handouts/references/ssa_example.pdf
+    @Test
+    public void testSSAExample() {
+        String src = """
+                func foo(x: Int, y: Int)->Int {
+                   var sum: Int
+                
+                   if (x >= y)
+                      return 0
+                
+                   sum = 0;
+                   while (x < y) {
+                      if (x / 2 * 2 == x) {
+                         sum = sum + 1
+                      }
+                      x = x + 1
+                   }
+                   return sum
+                }
+                """;
+        String result = compileSrc(src);
+        Assert.assertEquals("""
+func foo(x: Int,y: Int)->Int
+Reg #0 x 0
+Reg #1 y 1
+Reg #2 sum 2
+Reg #3 %t3 3
+Reg #4 %t4 4
+Reg #5 x_1 0
+Reg #6 y_1 1
+Reg #7 %t7 7
+Reg #8 %t8 8
+Reg #9 %t9 9
+Reg #10 %t10 10
+Reg #11 sum_1 2
+Reg #12 sum_2 2
+Reg #13 %t13 13
+Reg #14 x_2 0
+Reg #15 x_3 0
+Reg #16 y_2 1
+Reg #17 sum_3 2
+L0:
+    arg x
+    arg y
+    %t3 = x>=y
+    if %t3 goto L2 else goto L3
+L2:
+    ret 0
+    goto  L1
+L1:
+L3:
+    sum = 0
+    goto  L4
+L4:
+    sum_1 = phi(sum, sum_3)
+    x_1 = phi(x, x_3)
+    %t4 = x_1<y
+    if %t4 goto L5 else goto L6
+L5:
+    %t7 = x_1/2
+    %t8 = %t7*2
+    %t9 = %t8==x_1
+    if %t9 goto L7 else goto L8
+L7:
+    %t10 = sum_1+1
+    sum_2 = %t10
+    goto  L8
+L8:
+    sum_3 = phi(sum_1, sum_2)
+    %t13 = x_1+1
+    x_3 = %t13
+    goto  L4
+L6:
+    ret sum_1
+    goto  L1
+""", result);
+    }
+
+
 }
\ No newline at end of file
diff --git a/optvm/src/test/java/com/compilerprogramming/ezlang/compiler/TestSSATransform.java b/optvm/src/test/java/com/compilerprogramming/ezlang/compiler/TestSSATransform.java
index 2a91a12..39aec29 100644
--- a/optvm/src/test/java/com/compilerprogramming/ezlang/compiler/TestSSATransform.java
+++ b/optvm/src/test/java/com/compilerprogramming/ezlang/compiler/TestSSATransform.java
@@ -824,7 +824,6 @@ func foo(x: Int) {
     // http://users.csc.calpoly.edu/~akeen/courses/csc431/handouts/references/ssa_example.pdf
     @Test
     public void testSSAExample() {
-        // TODO
         String src = """
 func foo(x: Int, y: Int)->Int {
    var sum: Int
@@ -843,8 +842,117 @@ func foo(x: Int, y: Int)->Int {
 }
                 """;
         String result = compileSrc(src);
-        System.out.println(result);
-
+        Assert.assertEquals("""
+func foo
+Before SSA
+==========
+L0:
+    arg x
+    arg y
+    %t3 = x>=y
+    if %t3 goto L2 else goto L3
+L2:
+    ret 0
+    goto  L1
+L1:
+L3:
+    sum = 0
+    goto  L4
+L4:
+    %t4 = x<y
+    if %t4 goto L5 else goto L6
+L5:
+    %t5 = x/2
+    %t6 = %t5*2
+    %t7 = %t6==x
+    if %t7 goto L7 else goto L8
+L7:
+    %t8 = sum+1
+    sum = %t8
+    goto  L8
+L8:
+    %t9 = x+1
+    x = %t9
+    goto  L4
+L6:
+    ret sum
+    goto  L1
+After SSA
+=========
+L0:
+    arg x_0
+    arg y_0
+    %t3_0 = x_0>=y_0
+    if %t3_0 goto L2 else goto L3
+L2:
+    ret 0
+    goto  L1
+L1:
+L3:
+    sum_0 = 0
+    goto  L4
+L4:
+    sum_1 = phi(sum_0, sum_3)
+    x_1 = phi(x_0, x_2)
+    %t4_0 = x_1<y_0
+    if %t4_0 goto L5 else goto L6
+L5:
+    %t5_0 = x_1/2
+    %t6_0 = %t5_0*2
+    %t7_0 = %t6_0==x_1
+    if %t7_0 goto L7 else goto L8
+L7:
+    %t8_0 = sum_1+1
+    sum_2 = %t8_0
+    goto  L8
+L8:
+    sum_3 = phi(sum_1, sum_2)
+    %t9_0 = x_1+1
+    x_2 = %t9_0
+    goto  L4
+L6:
+    ret sum_1
+    goto  L1
+After exiting SSA
+=================
+L0:
+    arg x_0
+    arg y_0
+    %t3_0 = x_0>=y_0
+    if %t3_0 goto L2 else goto L3
+L2:
+    ret 0
+    goto  L1
+L1:
+L3:
+    sum_0 = 0
+    sum_1 = sum_0
+    x_1 = x_0
+    goto  L4
+L4:
+    %t4_0 = x_1<y_0
+    if %t4_0 goto L5 else goto L6
+L5:
+    %t5_0 = x_1/2
+    %t6_0 = %t5_0*2
+    %t7_0 = %t6_0==x_1
+    sum_3 = sum_1
+    if %t7_0 goto L7 else goto L8
+L7:
+    %t8_0 = sum_1+1
+    sum_2 = %t8_0
+    sum_3 = sum_2
+    goto  L8
+L8:
+    %t9_0 = x_1+1
+    x_2 = %t9_0
+    sum_1 = sum_3
+    x_1 = x_2
+    goto  L4
+L6:
+    ret sum_1
+    goto  L1
+""", result);
     }
 
     @Test
@@ -1069,7 +1177,81 @@ func foo(n: Int)->Int {
                 }
                 """;
         String result = compileSrc(src);
-        System.out.println(result);
+        Assert.assertEquals("""
+func foo
+Before SSA
+==========
+L0:
+    arg n
+    a = 1
+    b = 2
+    goto  L2
+L2:
+    %t4 = n>0
+    if %t4 goto L3 else goto L4
+L3:
+    t = a
+    a = b
+    b = t
+    %t5 = n-1
+    n = %t5
+    goto  L2
+L4:
+    ret a
+    goto  L1
+L1:
+After SSA
+=========
+L0:
+    arg n_0
+    a_0 = 1
+    b_0 = 2
+    goto  L2
+L2:
+    b_1 = phi(b_0, b_2)
+    a_1 = phi(a_0, a_2)
+    n_1 = phi(n_0, n_2)
+    %t4_0 = n_1>0
+    if %t4_0 goto L3 else goto L4
+L3:
+    t_0 = a_1
+    a_2 = b_1
+    b_2 = t_0
+    %t5_0 = n_1-1
+    n_2 = %t5_0
+    goto  L2
+L4:
+    ret a_1
+    goto  L1
+L1:
+After exiting SSA
+=================
+L0:
+    arg n_0
+    a_0 = 1
+    b_0 = 2
+    b_1 = b_0
+    a_1 = a_0
+    n_1 = n_0
+    goto  L2
+L2:
+    %t4_0 = n_1>0
+    if %t4_0 goto L3 else goto L4
+L3:
+    t_0 = a_1
+    a_2 = b_1
+    b_2 = t_0
+    %t5_0 = n_1-1
+    n_2 = %t5_0
+    b_1 = b_2
+    a_1 = a_2
+    n_1 = n_2
+    goto  L2
+L4:
+    ret a_1
+    goto  L1
+L1:
+""", result);
     }
 
     @Test
diff --git a/optvm/src/test/java/com/compilerprogramming/ezlang/interpreter/TestInterpreter.java b/optvm/src/test/java/com/compilerprogramming/ezlang/interpreter/TestInterpreter.java
index fcfe0f5..acb583c 100644
--- a/optvm/src/test/java/com/compilerprogramming/ezlang/interpreter/TestInterpreter.java
+++ b/optvm/src/test/java/com/compilerprogramming/ezlang/interpreter/TestInterpreter.java
@@ -4,15 +4,24 @@
 import com.compilerprogramming.ezlang.compiler.Options;
 import org.junit.Assert;
 import org.junit.Test;
+import org.junit.runner.RunWith;
+import org.junit.runners.Parameterized;
 
+import java.util.ArrayList;
+import java.util.Collection;
 import java.util.EnumSet;
+import java.util.List;
 
+@RunWith(Parameterized.class)
 public class TestInterpreter {
 
+    @Parameterized.Parameter
+    public EnumSet<Options> options;
+
     Value compileAndRun(String src, String mainFunction) {
-        return compileAndRun(src, mainFunction, Options.NONE);
+        return compileAndRun(src, mainFunction, options);
     }
-    Value compileAndRun(String src, String mainFunction, EnumSet<Options> options) {
+    Value compileAndRun(String src, String mainFunction, EnumSet<Options> optionsIgnored) {
         //options.add(Options.ISSA);
         var compiler = new Compiler();
         var typeDict = compiler.compileSrc(src, options);
@@ -22,6 +31,16 @@ Value compileAndRun(String src, String mainFunction, EnumSet<Options> options) {
         return interpreter.run(mainFunction);
     }
 
+    @Parameterized.Parameters
+    public static Collection<Object[]> data() {
+        List<Object[]> parameters = new ArrayList<>();
+        parameters.add(new Object[] { Options.NONE });
+        parameters.add(new Object[] { Options.OPT });
+        parameters.add(new Object[] { Options.OPT_ISSA });
+        return parameters;
+    }
+
+
     @Test
     public void testFunction1() {
         String src = """
diff --git a/registervm/src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java b/registervm/src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java
index 9cd5112..b0849e6 100644
--- a/registervm/src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java
+++ b/registervm/src/main/java/com/compilerprogramming/ezlang/compiler/CompiledFunction.java
@@ -176,14 +176,14 @@ private void compileBreak(AST.BreakStmt breakStmt) {
     }
 
     private void compileWhile(AST.WhileStmt whileStmt) {
-        BasicBlock loopBlock = createLoopHead();
+        BasicBlock loopHead = createLoopHead();
         BasicBlock bodyBlock = createBlock();
         BasicBlock exitBlock = createBlock();
         BasicBlock savedBreakTarget = currentBreakTarget;
         BasicBlock savedContinueTarget = currentContinueTarget;
         currentBreakTarget = exitBlock;
-        currentContinueTarget = loopBlock;
-        startBlock(loopBlock);
+        currentContinueTarget = loopHead;
+        startBlock(loopHead);
         boolean indexed = compileExpr(whileStmt.condition);
         if (indexed)
             codeIndexedLoad();
@@ -192,7 +192,7 @@ private void compileWhile(AST.WhileStmt whileStmt) {
         startBlock(bodyBlock);
         compileStatement(whileStmt.stmt);
         if (!isBlockTerminated(currentBlock))
-            jumpTo(loopBlock);
+            jumpTo(loopHead);
         startBlock(exitBlock);
         currentContinueTarget = savedContinueTarget;
         currentBreakTarget = savedBreakTarget;
@@ -217,16 +217,16 @@ private void startBlock(BasicBlock block) {
     }
 
     private void compileIf(AST.IfElseStmt ifElseStmt) {
-        BasicBlock ifBlock = createBlock();
+        BasicBlock thenBlock = createBlock();
         boolean needElse = ifElseStmt.elseStmt != null;
         BasicBlock elseBlock = needElse ? createBlock() : null;
         BasicBlock exitBlock = createBlock();
         boolean indexed = compileExpr(ifElseStmt.condition);
         if (indexed)
             codeIndexedLoad();
-        code(new Instruction.ConditionalBranch(currentBlock, pop(), ifBlock, needElse ? elseBlock : exitBlock));
+        code(new Instruction.ConditionalBranch(currentBlock, pop(), thenBlock, needElse ? elseBlock : exitBlock));
         assert vstackEmpty();
-        startBlock(ifBlock);
+        startBlock(thenBlock);
         compileStatement(ifElseStmt.ifStmt);
         if (!isBlockTerminated(currentBlock))
             jumpTo(exitBlock);
@@ -363,23 +363,6 @@ private boolean compileSetFieldExpr(AST.SetFieldExpr setFieldExpr) {
         return false;
     }
 
-    private void codeNew(Type type) {
-        var temp = createTemp(type);
-        if (type instanceof Type.TypeArray typeArray) {
-            code(new Instruction.NewArray(typeArray, temp));
-        }
-        else if (type instanceof Type.TypeStruct typeStruct) {
-            code(new Instruction.NewStruct(typeStruct, temp));
-        }
-        else
-            throw new CompilerException("Unexpected type: " + type);
-    }
-
-    private void codeStoreAppend() {
-        var operand = pop();
-        code(new Instruction.AStoreAppend((Operand.RegisterOperand) top(), operand));
-    }
-
     private boolean compileNewExpr(AST.NewExpr newExpr) {
         codeNew(newExpr.type);
         if (newExpr.initExprList != null && !newExpr.initExprList.isEmpty()) {
@@ -437,7 +420,6 @@ private boolean codeBoolean(AST.BinaryExpr binaryExpr) {
         return false;
     }
 
-
     private boolean compileBinaryExpr(AST.BinaryExpr binaryExpr) {
         String opCode = binaryExpr.op.str;
         if (opCode.equals("&&") ||
@@ -581,15 +563,17 @@ private Operand top() {
         return virtualStack.getLast();
     }
 
+    private boolean vstackEmpty() {
+        return virtualStack.isEmpty();
+    }
+
     private Operand.TempRegisterOperand codeIndexedLoad() {
         Operand indexed = pop();
         var temp = createTemp(indexed.type);
-        if (indexed instanceof Operand.LoadIndexedOperand loadIndexedOperand) {
+        if (indexed instanceof Operand.LoadIndexedOperand loadIndexedOperand)
             code(new Instruction.ArrayLoad(loadIndexedOperand, temp));
-        }
-        else if (indexed instanceof Operand.LoadFieldOperand loadFieldOperand) {
+        else if (indexed instanceof Operand.LoadFieldOperand loadFieldOperand)
             code(new Instruction.GetField(loadFieldOperand, temp));
-        }
         else
             code(new Instruction.Move(indexed, temp));
         return temp;
@@ -598,17 +582,28 @@ else if (indexed instanceof Operand.LoadFieldOperand loadFieldOperand) {
     private void codeIndexedStore() {
         Operand value = pop();
         Operand indexed = pop();
-        if (indexed instanceof Operand.LoadIndexedOperand loadIndexedOperand) {
+        if (indexed instanceof Operand.LoadIndexedOperand loadIndexedOperand)
             code(new Instruction.ArrayStore(value, loadIndexedOperand));
-        }
-        else if (indexed instanceof Operand.LoadFieldOperand loadFieldOperand) {
+        else if (indexed instanceof Operand.LoadFieldOperand loadFieldOperand)
             code(new Instruction.SetField(value, loadFieldOperand));
-        }
         else
             code(new Instruction.Move(value, indexed));
     }
 
-    private boolean vstackEmpty() {
-        return virtualStack.isEmpty();
+    private void codeNew(Type type) {
+        var temp = createTemp(type);
+        if (type instanceof Type.TypeArray typeArray)
+            code(new Instruction.NewArray(typeArray, temp));
+        else if (type instanceof Type.TypeStruct typeStruct)
+            code(new Instruction.NewStruct(typeStruct, temp));
+        else
+            throw new CompilerException("Unexpected type: " + type);
     }
+
+    private void codeStoreAppend() {
+        var operand = pop();
+        code(new Instruction.AStoreAppend((Operand.RegisterOperand) top(), operand));
+    }
+
+
 }