Chapter20 initial push

37 files changed, 8319 insertions, 0 deletions

diff --git a/chapter20/src/test/java/com/seaofnodes/simple/BrainFuckTest.java b/chapter20/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
new file mode 100644
index 00000000..8f09cb3d
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
@@ -0,0 +1,69 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import java.nio.charset.StandardCharsets;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class BrainFuckTest {
+
+    @Test
+    public void testBrainfuck() {
+        var program = "++++++++[>++++[>++>+++>+++>+<<<<-]>+>+>->>+[<]<-]>>.>---.+++++++..+++.>>.<-.<.+++.------.--------.>>+.>++.".getBytes(StandardCharsets.UTF_8);
+        var encoded = new StringBuilder("u8[] !program = new u8[").append(program.length).append("];");
+        for (int i = 0; i < program.length; i++) {
+            int value = program[i] & 0xFF;
+            encoded.append("program[").append(i).append("] = ").append(value).append(";");
+        }
+
+        CodeGen code = new CodeGen(
+                encoded + """
+
+int d = 0;
+u8[] !output = new u8[0];
+u8[] !data = new u8[100];
+
+for( int pc = 0; pc < program#; pc++ ) {
+    var command = program[pc];
+    if (command == 62) {
+        d++;
+    } else if (command == 60) {
+        d--;
+    } else if (command == 43) {
+        data[d]++;
+    } else if (command == 45) {
+        data[d]--;
+    } else if (command == 46) {
+        // Output a byte; increase the output array size
+        var old = output;
+        output = new u8[output# + 1];
+        for( int i = 0; i < old#; i++ )
+            output[i] = old[i];
+        output[old#] = data[d]; // Add the extra byte on the end
+    } else if (command == 44) {
+        data[d] = 42;
+    } else if (command == 91) {
+        if (data[d] == 0) {
+            for( int d = 1; d > 0; ) {
+                command = program[++pc];
+                if (command == 91) d++;
+                if (command == 93) d--;
+            }
+        }
+    } else if (command == 93) {
+        if (data[d]) {
+            for( int d = 1; d > 0; ) {
+                command = program[--pc];
+                if (command == 93) d++;
+                if (command == 91) d--;
+            }
+        }
+    }
+}
+return output;
+                """);
+        code.parse().opto().typeCheck()/*.instSelect("x86_64_v2", "SystemV")*/.GCM().localSched();
+        assertEquals("Hello World!\n", Eval2.eval(code, 0, 10000));
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter01Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter01Test.java
new file mode 100644
index 00000000..934eda76
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter01Test.java
@@ -0,0 +1,94 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter01Test {
+
+    @Test
+    public void testSimpleProgram() {
+        CodeGen code = new CodeGen("return 1;").parse();
+        Node expr = code.expr();
+        if( expr instanceof ConstantNode con ) {
+            assertEquals(code._start,con.in(0));
+            assertEquals(TypeInteger.constant(1), con._type);
+        } else {
+            fail();
+        }
+    }
+
+    @Test
+    public void testZero() {
+        CodeGen code = new CodeGen("return 0;");
+        code.parse();
+        for( Node use : code._start._outputs )
+            if( use instanceof ConstantNode con && con._type instanceof TypeInteger )
+                assertEquals(TypeInteger.constant(0),con._type);
+    }
+
+    @Test
+    public void testBad1() {
+        try {
+            new CodeGen("ret;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Undefined name 'ret'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testBad2() {
+        try {
+            new CodeGen("return 0123;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error: integer values cannot start with '0'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testNotBad3() {
+        // this test used to fail in chapter 1
+        assertEquals("return 12;", new CodeGen("return - -12;").parse()._stop.print());
+    }
+
+    @Test
+    public void testBad4() {
+        try {
+            new CodeGen("return 100").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, expected ;: ",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testNotBad5() {
+        // this test used to fail in chapter 1
+        assertEquals("return -100;", new CodeGen("return -100;").parse()._stop.print());
+    }
+
+    @Test
+    public void testBad6() {
+        try {
+            new CodeGen("return100;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Undefined name 'return100'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testBad7() {
+        try {
+            new CodeGen("return 1;}").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, unexpected: }",e.getMessage());
+        }
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter02Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter02Test.java
new file mode 100644
index 00000000..d8607c32
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter02Test.java
@@ -0,0 +1,60 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter02Test {
+
+    @Test
+    public void testParseGrammar() {
+        CodeGen code = new CodeGen("return 1+2*3+-5;");
+        code.parse(); // No more disable peepholes
+        assertEquals("return 2;", code.print());
+    }
+
+    @Test
+    public void testAddPeephole() {
+        CodeGen code = new CodeGen("return 1+2;");
+        code.parse();
+        assertEquals("return 3;", code.print());
+    }
+
+    @Test
+    public void testSubPeephole() {
+        CodeGen code = new CodeGen("return 1-2;");
+        code.parse();
+        assertEquals("return -1;", code.print());
+    }
+
+    @Test
+    public void testMulPeephole() {
+        CodeGen code = new CodeGen("return 2*3;");
+        code.parse();
+        assertEquals("return 6;", code.print());
+    }
+
+    @Test
+    public void testDivPeephole() {
+        CodeGen code = new CodeGen("return 6/3;");
+        code.parse();
+        assertEquals("return 2;", code.print());
+    }
+
+    @Test
+    public void testMinusPeephole() {
+        CodeGen code = new CodeGen("return 6/-3;");
+        code.parse();
+        assertEquals("return -2;", code.print());
+    }
+
+    @Test
+    public void testExample() {
+        CodeGen code = new CodeGen("return 1+2*3+-5;");
+        code.parse();
+        assertEquals("return 2;", code.print());
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter03Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter03Test.java
new file mode 100644
index 00000000..4f9b2490
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter03Test.java
@@ -0,0 +1,73 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter03Test {
+
+    @Test
+    public void testVarDecl() {
+        CodeGen code = new CodeGen("int a=1; return a;");
+        code.parse(); assertEquals("return 1;", code.print());
+    }
+
+    @Test
+    public void testVarAdd() {
+        CodeGen code = new CodeGen("int a=1; int b=2; return a+b;");
+        code.parse();
+        assertEquals("return 3;", code.print());
+    }
+
+    @Test
+    public void testVarScope() {
+        CodeGen code = new CodeGen("int a=1; int b=2; int c=0; { int b=3; c=a+b; } return c;");
+        code.parse();
+        assertEquals("return 4;", code.print());
+    }
+
+    @Test
+    public void testVarScopeNoPeephole() {
+        CodeGen code = new CodeGen("int a=1; int b=2; int !c=0; { int b=3; c=a+b;  } return c; ");
+        code.parse();           // Peepholes always run now
+        assertEquals("return 4;", code.print());
+    }
+
+    @Test
+    public void testVarDist() {
+        CodeGen code = new CodeGen("int x0=1; int y0=2; int x1=3; int y1=4; return (x0-x1)*(x0-x1) + (y0-y1)*(y0-y1); ");
+        code.parse();
+        assertEquals("return 8;", code.print());
+    }
+
+    @Test
+    public void testSelfAssign() {
+        try {
+            new CodeGen("int a=a; return a;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Undefined name 'a'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testRedeclareVar() {
+        try {
+            new CodeGen("int a=1; int b=2; int c=0; int b=3; c=a+b;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Redefining name 'b'",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testBad1() {
+        try {
+            new CodeGen("int a=1; int b=2; int !c=0; { int b=3; c=a+b;").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("Syntax error, expected }: ",e.getMessage());
+        }
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter04Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter04Test.java
new file mode 100644
index 00000000..d09b1748
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter04Test.java
@@ -0,0 +1,130 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Test;
+import org.junit.Ignore;
+
+import static org.junit.Assert.*;
+
+public class Chapter04Test {
+
+    @Test
+    public void testPeephole() {
+        CodeGen code = new CodeGen("return 1+arg+2; ");
+        code.parse();
+        assertEquals("return (arg+3);", code.print());
+    }
+
+    @Test
+    public void testPeephole2() {
+        CodeGen code = new CodeGen("return (1+arg)+2;");
+        code.parse();
+        assertEquals("return (arg+3);", code.print());
+    }
+
+    @Test
+    public void testAdd0() {
+        CodeGen code = new CodeGen("return 0+arg;");
+        code.parse();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void testAddAddMul() {
+        CodeGen code = new CodeGen("return arg+0+arg;");
+        code.parse();
+        assertEquals("return (arg<<1);", code.print());
+    }
+
+    @Test
+    public void testPeephole3() {
+        CodeGen code = new CodeGen("return 1+arg+2+arg+3; ");
+        code.parse();
+        assertEquals("return ((arg<<1)+6);", code.print());
+    }
+
+    @Test
+    public void testMul1() {
+        CodeGen code = new CodeGen("return 1*arg;");
+        code.parse();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void testVarArg() {
+        CodeGen code = new CodeGen("return arg; ");
+        code.parse();
+        assertTrue(code.ctrl() instanceof  FunNode);
+        assertTrue(code.expr() instanceof ParmNode);
+    }
+
+    // Adding functions means `main` does not constant fold the incoming arg value
+    @Ignore @Test
+    public void testConstantArg() {
+        CodeGen code = new CodeGen("return arg; ", TypeInteger.constant(2), 123L).parse();
+        assertEquals("return 2;", code.expr().in(1).toString());
+    }
+
+    @Test
+    public void testCompEq() {
+        CodeGen code = new CodeGen("return 3==3; ");
+        code.parse();
+        assertEquals("return 1;", code.print());
+    }
+
+    @Test
+    public void testCompEq2() {
+        CodeGen code = new CodeGen("return 3==4; ");
+        code.parse();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testCompNEq() {
+        CodeGen code = new CodeGen("return 3!=3; ");
+        code.parse();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testCompNEq2() {
+        CodeGen code = new CodeGen("return 3!=4; ");
+        code.parse();
+        assertEquals("return 1;", code.print());
+    }
+
+    @Test
+    public void testBug1() {
+        CodeGen code = new CodeGen("int a=arg+1; int !b=a; b=1; return a+2; ");
+        code.parse();
+        assertEquals("return (arg+3);", code.print());
+    }
+
+    @Test
+    public void testBug2() {
+        CodeGen code = new CodeGen("int !a=arg+1; a=a; return a; ");
+        code.parse();
+        assertEquals("return (arg+1);", code.print());
+    }
+
+    @Test
+    public void testBug3() {
+        try { new CodeGen("inta=1; return a;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Undefined name 'inta'",e.getMessage()); }
+    }
+
+    @Test
+    public void testBug4() {
+        CodeGen code = new CodeGen("return -arg;");
+        code.parse();
+        assertEquals("return (-arg);", code.print());
+    }
+
+    @Test
+    public void testBug5() {
+        CodeGen code = new CodeGen("return arg--2;");
+        code.parse();
+        assertEquals("return (arg--2);", code.print());
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter05Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter05Test.java
new file mode 100644
index 00000000..86ec4136
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter05Test.java
@@ -0,0 +1,185 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter05Test {
+
+    @Test
+    public void testIfStmt() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+if (arg == 1)
+    a = arg+2;
+else {
+    a = arg-3;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,(arg+2),(arg-3));", code.print());
+    }
+
+    @Test
+    public void testTest() {
+        CodeGen code = new CodeGen(
+"""
+int c = 3;
+int b = 2;
+if (arg == 1) {
+    b = 3;
+    c = 4;
+}
+return c;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,4,3);", code.print());
+    }
+
+    @Test
+    public void testReturn2() {
+        CodeGen code = new CodeGen(
+"""
+if( arg==1 )
+    return 3;
+else
+    return 4;
+""");
+        code.parse();
+        assertEquals("return Phi(Region,3,4);", code.print());
+    }
+
+    @Test
+    public void testIfMergeB() {
+        CodeGen code = new CodeGen(
+"""
+int a=arg+1;
+int b=0;
+if( arg==1 )
+    b=a;
+else
+    b=a+1;
+return a+b;""");
+        code.parse().opto();
+        assertEquals("return ((arg<<1)+Phi(Region,2,3));", code.print());
+    }
+
+    @Test
+    public void testIfMerge2() {
+        CodeGen code = new CodeGen(
+"""
+int a=arg+1;
+int b=arg+2;
+if( arg==1 )
+    b=b+a;
+else
+    a=b+1;
+return a+b;""");
+        code.parse().opto();
+        assertEquals("return ((Phi(Region,(arg<<1),arg)+arg)+Phi(Region,4,5));", code.print());
+    }
+
+    @Test
+    public void testMerge3() {
+        CodeGen code = new CodeGen(
+"""
+int a=1;
+if( arg==1 )
+    if( arg==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Region,2,3),Phi(Region,4,5));", code.print());
+    }
+
+    @Test
+    public void testMerge4() {
+        CodeGen code = new CodeGen(
+"""
+int a=0;
+int b=0;
+if( arg )
+    a=1;
+if( arg==0 )
+    b=2;
+return arg+a+b;
+""");
+        code.parse().opto();
+        assertEquals("return ((arg+Phi(Region,1,0))+Phi(Region,2,0));", code.print());
+    }
+
+    @Test
+    public void testMerge5() {
+        CodeGen code = new CodeGen(
+"""
+int a=arg==2;
+if( arg==1 )
+{
+    a=arg==3;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return (arg==Phi(Region,3,2));", code.print());
+    }
+
+    @Test
+    public void testTrue() {
+      CodeGen code = new CodeGen("return true;").parse();
+      assertEquals("return 1;",code.print());
+    }
+
+    @Test
+    public void testHalfDef() {
+        try { new CodeGen("if( arg==1 ) int b=2; return b;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Cannot define a 'b' on one arm of an if",e.getMessage()); }
+    }
+
+    @Test
+    public void testHalfDef2() {
+        try { new CodeGen("if( arg==1 ) { int b=2; } else { int b=3; } return b;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Undefined name 'b'",e.getMessage()); }
+    }
+
+    @Test
+    public void testRegress1() {
+        try { new CodeGen("if(arg==2) int a=1; else int b=2; return a;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Cannot define a 'a' on one arm of an if",e.getMessage()); }
+    }
+
+
+    @Test
+    public void testBadNum() {
+        try { new CodeGen("return 1-;").parse();  fail(); }
+        catch( RuntimeException e ) { assertEquals("Syntax error, expected an identifier or expression: ;",e.getMessage()); }
+    }
+
+    @Test
+    public void testKeyword1() {
+        try { new CodeGen("int true=0; return true;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Expected an identifier, found 'true'",e.getMessage()); }
+    }
+
+    @Test
+    public void testKeyword2() {
+        try { new CodeGen("int else=arg; if(else) else=2; else else=1; return else;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Expected an identifier, found 'else'",e.getMessage()); }
+    }
+
+    @Test
+    public void testKeyword3() {
+        try { new CodeGen("int a=1; ififif(arg);a=2;return a;").parse(); fail(); }
+        catch( RuntimeException e ) { assertEquals("Undefined name 'ififif'",e.getMessage()); }
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter06Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter06Test.java
new file mode 100644
index 00000000..117531f0
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter06Test.java
@@ -0,0 +1,304 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter06Test {
+
+    @Test
+    public void testPeepholeReturn() {
+        CodeGen code = new CodeGen("""
+if( true ) return 2;
+return 1;
+""");
+        code.parse().opto();
+        assertEquals("return 2;", code.print());
+        assertTrue(code.ctrl() instanceof FunNode);
+    }
+
+    @Test
+    public void testPeepholeRotate() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+if (arg)
+    a = 2;
+return (arg < a) < 3; // Because (arg < a) is a bool/uint1/[0-1], its always less than 3
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+    }
+
+    @Test
+    public void testPeepholeCFG() {
+        CodeGen code = new CodeGen(
+"""
+int a=1;
+if( true )
+  a=2;
+else
+  a=3;
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return 2;", code.print());
+        assertTrue(code.ctrl() instanceof FunNode);
+    }
+
+    @Test
+    public void testIfIf() {
+        CodeGen code = new CodeGen(
+"""
+int a=1;
+if( arg!=1 )
+    a=2;
+else
+    a=3;
+int b=4;
+if( a==2 )
+    b=42;
+else
+    b=5;
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,42,5);", code.print());
+    }
+
+    @Test
+    public void testIfArgIf() {
+        CodeGen code = new CodeGen(
+"""
+int a=1;
+if( 1==1 )
+    a=2;
+else
+    a=3;
+int b=4;
+if( arg==2 )
+    b=a;
+else
+    b=5;
+return b;""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,2,5);", code.print());
+    }
+
+    @Test
+    public void testMerge3With2() {
+        CodeGen code = new CodeGen(
+"""
+arg=2;
+int a=1;
+if( arg==1 )
+    if( arg==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(2), 123L).parse().opto();
+        assertEquals("return 5;", code.print());
+    }
+
+    @Test
+    public void testMerge3With1() {
+        CodeGen code = new CodeGen(
+"""
+arg=1;
+int a=1;
+if( arg==1 )
+    if( arg==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(1), 123L).parse().opto();
+        assertEquals("return 3;", code.print());
+    }
+
+    @Test
+    public void testMerge3Peephole() {
+        CodeGen code = new CodeGen(
+"""
+int a=1;
+if( arg==1 )
+    if( 1==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,3,Phi(Region,4,5));", code.print());
+    }
+
+    @Test
+    public void testMerge3Peephole1() {
+        CodeGen code = new CodeGen(
+"""
+arg=1;
+int a=1;
+if( arg==1 )
+    if( 1==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(1), 123L);
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+    }
+
+    @Test
+    public void testMerge3Peephole3() {
+        CodeGen code = new CodeGen(
+"""
+arg=3;
+int a=1;
+if( arg==1 )
+    if( 1==2 )
+        a=2;
+    else
+        a=3;
+else if( arg==3 )
+    a=4;
+else
+    a=5;
+return a;
+""", TypeInteger.constant(3), 123L);
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+    }
+
+    @Test
+    public void testDemo1NonConst() {
+        CodeGen code = new CodeGen("""
+int a = 0;
+int b = 1;
+if( arg ) {
+    a = 2;
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,4,1);", code.print());
+    }
+
+
+    @Test
+    public void testDemo1True() {
+        CodeGen code = new CodeGen(
+"""
+arg=1;
+int a = 0;
+int b = 1;
+if( arg ) {
+    a = 2;
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b;
+""", TypeInteger.constant(1), 123L);
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+    }
+
+    @Test
+    public void testDemo1False() {
+        CodeGen code = new CodeGen(
+"""
+arg=0;
+int a = 0;
+int b = 1;
+if( arg ) {
+    a = 2;
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b;
+""", TypeInteger.constant(0), 123L);
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+    }
+
+    @Test
+    public void testDemo2NonConst() {
+        CodeGen code = new CodeGen("""
+int a = 0;
+int b = 1;
+int c = 0;
+if( arg ) {
+    a = 1;
+    if( arg==2 ) { c=2; } else { c=3; }
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b+c;
+""");
+        code.parse().opto();
+        assertEquals("return (Phi(Region,Phi(Region,2,3),0)+Phi(Region,3,1));", code.print());
+    }
+
+
+    @Test
+    public void testDemo2True() {
+        CodeGen code = new CodeGen(
+"""
+arg=1;
+int a = 0;
+int b = 1;
+int c = 0;
+if( arg ) {
+    a = 1;
+    if( arg==2 ) { c=2; } else { c=3; }
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b+c;
+""", TypeInteger.constant(1), 123L);
+        code.parse().opto();
+        assertEquals("return 6;", code.print());
+    }
+
+    @Test
+    public void testDemo2arg2() {
+        CodeGen code = new CodeGen(
+"""
+arg=2;
+int a = 0;
+int b = 1;
+int c = 0;
+if( arg ) {
+    a = 1;
+    if( arg==2 ) { c=2; } else { c=3; }
+    if( arg ) { b = 2; }
+    else b = 3;
+}
+return a+b+c;
+""", TypeInteger.constant(2), 123L);
+        code.parse().opto();
+        assertEquals("return 5;", code.print());
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter07Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter07Test.java
new file mode 100644
index 00000000..6d6a3ce7
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter07Test.java
@@ -0,0 +1,221 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter07Test {
+
+    @Test
+    public void testExample() {
+        CodeGen code = new CodeGen(
+"""
+while(arg < 10) {
+    arg = arg + 1;
+}
+return arg;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,arg,(Phi_arg+1));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testRegression() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+if(arg){}else{
+    while(a < 10) {
+        a = a + 1;
+    }
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,1,Phi(Loop,1,(Phi_a+1)));", code.print());
+    }
+
+    @Test
+    public void testWhileNested() {
+        CodeGen code = new CodeGen(
+"""
+int sum = 0;
+int i = 0;
+while(i < arg) {
+    i = i + 1;
+    int j = 0;
+    while( j < arg ) {
+        sum = sum + j;
+        j = j + 1;
+    }
+}
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,Phi(Loop,Phi_sum,(Phi_sum+Phi(Loop,0,(Phi_j+1)))));", code.print());
+    }
+
+    @Test
+    public void testWhileScope() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+int b = 2;
+while(a < 10) {
+    if (a == 2) a = 3;
+    else b = 4;
+}
+return b;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,2,Phi(Region,Phi_b,4));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhileNestedIfAndInc() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+int b = 2;
+while(a < 10) {
+    if (a == 2) a = 3;
+    else b = 4;
+    b = b + 1;
+    a = a + 1;
+}
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,2,(Phi(Region,Phi_b,4)+1));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+
+    @Test
+    public void testWhile() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(a < 10) {
+    a = a + 1;
+    a = a + 2;
+}
+return a;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhilePeep() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(a < 10) {
+    a = a + 1;
+    a = a + 2;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile2() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(arg) a = 2;
+return a;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,1,2);", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile2Peep() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(arg) a = 2;
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,1,2);", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile3() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(a < 10) {
+    int b = a + 1;
+    a = b + 2;
+}
+return a;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile3Peep() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+while(a < 10) {
+    int b = a + 1;
+    a = b + 2;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile4() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+int b = 2;
+while(a < 10) {
+    int b = a + 1;
+    a = b + 2;
+}
+return a;
+""");
+        code.parse();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testWhile4Peep() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+int b = 2;
+while(a < 10) {
+    int b = a + 1;
+    a = b + 2;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,1,(Phi_a+3));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter08Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter08Test.java
new file mode 100644
index 00000000..350df18b
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter08Test.java
@@ -0,0 +1,207 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.*;
+import org.junit.Assert;
+import org.junit.Test;
+
+import static org.junit.Assert.*;
+
+public class Chapter08Test {
+
+    @Test
+    public void testEx6() {
+        CodeGen code = new CodeGen(
+                """
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 5)
+        break;
+    if (arg == 6)
+        break;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add),Add);", code.print());
+        assertTrue(code.ctrl() instanceof RegionNode);
+        Assert.assertEquals( "5", Eval2.eval(code, 1));
+        Assert.assertEquals("10", Eval2.eval(code, 6));
+    }
+
+
+    @Test
+    public void testEx5() {
+        CodeGen code = new CodeGen(
+                """
+int a = 1;
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 5)
+        continue;
+    if (arg == 7)
+        continue;
+    a = a + 1;
+}
+return a;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Loop,1,Phi(Region,Phi_a,(Phi_a+1)));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+
+    @Test
+    public void testEx4() {
+        CodeGen code = new CodeGen(
+                """
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 5)
+        continue;
+    if (arg == 6)
+        break;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add);", code.print());
+        assertTrue(code.ctrl() instanceof RegionNode);
+    }
+
+    @Test
+    public void testEx3() {
+        CodeGen code = new CodeGen(
+                """
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 6)
+        break;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Loop,arg,(Phi_arg+1)),Add);", code.print());
+        assertTrue(code.ctrl() instanceof RegionNode);
+    }
+
+
+    @Test
+    public void testEx2() {
+        CodeGen code = new CodeGen(
+                """
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 5)
+        continue;
+    if (arg == 6)
+        continue;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Loop,arg,(Phi_arg+1));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+
+    @Test
+    public void testEx1() {
+        CodeGen code = new CodeGen(
+                """
+while(arg < 10) {
+    arg = arg + 1;
+    if (arg == 5)
+        continue;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Loop,arg,(Phi_arg+1));", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode);
+    }
+
+    @Test
+    public void testRegress1() {
+        CodeGen code = new CodeGen(
+                """
+while( arg < 10 ) {
+    int a = arg+2;
+    if( a > 4 )
+        break;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void testRegress2() {
+        CodeGen code = new CodeGen("if(1) return 0;  else while(arg>- -arg) arg=arg+1; return 0;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testBreakOutsideLoop() {
+        try {
+            new CodeGen("""
+if(arg <= 10) {
+    break;
+    arg = arg + 1;
+}
+return arg;
+""").parse();
+            fail();
+        } catch( RuntimeException e ) {
+            assertEquals("No active loop for a break or continue",e.getMessage());
+        }
+    }
+
+    @Test
+    public void testRegress3() {
+        CodeGen code = new CodeGen("""
+while(arg < 10) {
+    break;
+}
+return arg;
+""");
+        code.parse().opto();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void testRegress4() {
+        CodeGen code = new CodeGen("""
+int a = 1;
+while(arg < 10) {
+    a = a + 1;
+    if (arg > 2) {
+        int a = 17;
+        break;
+    }
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Loop,1,(Phi_a+1)),Add);", code.print());
+        assertTrue(code.ctrl() instanceof RegionNode);
+    }
+
+    @Test
+    public void testRegress5() {
+        CodeGen code = new CodeGen("""
+int a = 1;
+while(1) {
+    a = a + 1;
+    if (a<10) continue;
+    break;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return (Phi(Loop,1,Add)+1);", code.print());
+        assertTrue(code.ctrl() instanceof CProjNode prj && prj._idx==1 );
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter09Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter09Test.java
new file mode 100644
index 00000000..10f4a78b
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter09Test.java
@@ -0,0 +1,296 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import com.seaofnodes.simple.type.Type;
+import com.seaofnodes.simple.type.TypeInteger;
+import org.junit.Assert;
+import org.junit.Test;
+import org.junit.Ignore;
+
+import static org.junit.Assert.*;
+
+public class Chapter09Test {
+
+    @Test
+    @Ignore
+    public void testJig() {
+        CodeGen code = new CodeGen("""
+int v0=0;
+arg=0;
+while(v0) {
+        while(1) if(arg*arg*0==0) {}
+                while(0) {}
+    arg=1;
+}
+return 0;
+                """);
+        code.parse().opto();
+    }
+
+    @Test
+    public void testGVN1() {
+        CodeGen code = new CodeGen(
+                """
+int x = arg + arg;
+if(arg < 10) {
+    return arg + arg;
+}
+else {
+    x = x + 1;
+}
+return x;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Region,(arg<<1),(Shl+1));", code.print());
+        Assert.assertEquals( "2", Eval2.eval(code,  1));
+        Assert.assertEquals("23", Eval2.eval(code, 11));
+    }
+
+    @Test
+    public void testGVN2() {
+        CodeGen code = new CodeGen("return arg*arg-arg*arg;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        Assert.assertEquals("0", Eval2.eval(code,  1, 1));
+    }
+
+    @Test
+    public void testWorklist1() {
+        CodeGen code = new CodeGen("""
+int step = 1;
+while (arg < 10) {
+    arg = arg + step + 1;
+}
+return arg;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,arg,(Phi_arg+2));", code.print());
+        Assert.assertEquals("11", Eval2.eval(code,  1));
+    }
+
+    @Test
+    public void testWorklist2() {
+        CodeGen code = new CodeGen(
+                """
+int cond = 0;
+int one = 1;
+while (arg < 10) {
+    if (cond) one = 2;
+    arg = arg + one*3 + 1;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return Phi(Loop,arg,(Phi_arg+4));", code.print());
+        Assert.assertEquals("13", Eval2.eval(code,  1));
+    }
+
+    @Test
+    public void testWorklist3() {
+        CodeGen code = new CodeGen(
+                """
+int v1 = 0;
+int v2 = 0;
+int v3 = 0;
+int v4 = 0;
+int v5 = 0;
+int v6 = 0;
+int v7 = 0;
+int v8 = 0;
+while (arg) {
+    if (v1) v2 = 1;
+    if (v2) v3 = 1;
+    if (v3) v4 = 1;
+    if (v4) v5 = 1;
+    if (v5) v6 = 1;
+    if (v6) v7 = 1;
+    if (v7) v8 = 1;
+    arg = arg + v8 + 1;
+}
+return arg;
+                """);
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testRegionPeepBug() {
+        CodeGen code = new CodeGen(
+                """
+int v0=0;
+int v1=0;
+while(v1+arg) {
+    arg=0;
+    int v2=v0;
+    while(arg+1) {}
+    v0=1;
+    v1=v2;
+}
+                """);
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testWhile0() {
+        CodeGen code = new CodeGen("while(0) continue; if(0) arg=0;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testWhile1() {
+        CodeGen code = new CodeGen("""
+if(0) while(0) {
+    int arg=arg;
+    while(0) {}
+}
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+
+    @Test
+    public void testPrecedence() {
+        CodeGen code = new CodeGen("return 3-1+2;");
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+    }
+
+    @Test
+    public void testSwap2() {
+        CodeGen code = new CodeGen("return 1+(1+1);");
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+    }
+
+
+    @Test
+    public void testFuzz0() {
+        CodeGen code = new CodeGen("""
+int one = 1;
+int a = 0;
+int zero = 0;
+while(arg) {
+    a = -(one + a + 2);
+    arg = arg + 1;
+    one = one + zero;
+}
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(-(Phi_a+3)));", code.print());
+    }
+
+    @Test
+    public void testFuzz1() {
+        CodeGen code = new CodeGen("""
+while(1) {}
+while(arg) break;
+while(arg) arg=0;
+arg=0;
+int v0=0!=0<-0;
+return -0+0+0;
+""");
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+
+    @Test
+    public void testFuzz2() {
+        CodeGen code = new CodeGen("return 0+-0;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testFuzz3() {
+        CodeGen code = new CodeGen("int v0=0; while(0==69) while(v0) return 0;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testFuzz4() {
+        CodeGen code = new CodeGen("""
+while(1) {
+    arg=0<=0;
+    if(1<0) while(arg==-0) arg=arg-arg;
+}
+""");
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+    @Test
+    public void testFuzz5() {
+        CodeGen code = new CodeGen("""
+{
+    int v0=0;
+    while(1)
+            int v1=0--0;
+    while(v0)
+        break;
+    while(-v0) {
+        while(0+0+v0) continue;
+        break;
+    }
+    if(-0!=-0+0+v0) while(0+0+0+0)
+                break;
+}
+return 0!=0;
+""");
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+    @Test
+    public void testFuzz6() {
+        CodeGen code = new CodeGen(
+"""
+int v0=0;
+while(0==1) while(v0)
+        v0=1+v0;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testFuzz7() {
+        CodeGen code = new CodeGen("""
+while(1) {}
+int v0=0;
+while(v0)
+    {}
+int v1=0;
+while(1)
+        v1=1;
+return v1+v0;
+                                   """);
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+    @Test
+    public void testFuzz8() {
+        CodeGen code = new CodeGen("while(arg) arg = arg - 1;  return arg;");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testMeet() {
+        Type t1 = Type.TOP;
+        Type t2 = TypeInteger.TOP;
+        Assert.assertEquals(TypeInteger.TOP, t1.meet(t2));
+        Assert.assertEquals(TypeInteger.TOP, t2.meet(t1));
+        t1 = Type.BOTTOM;
+        t2 = TypeInteger.BOT;
+        Assert.assertEquals(Type.BOTTOM, t1.meet(t2));
+        Assert.assertEquals(Type.BOTTOM, t2.meet(t1));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter10Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter10Test.java
new file mode 100644
index 00000000..02029b3f
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter10Test.java
@@ -0,0 +1,396 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter10Test {
+
+    @Test
+    public void testFuzzer() {
+        CodeGen code = new CodeGen(
+"""
+int a = arg/3;
+int b = arg*5;
+int x = arg*7;
+int y = arg/11;
+int p; int g; int h;
+if( (arg/13)==0 ) {
+    p = x + y;
+    g = x;
+    h = y;
+} else {
+    p = a + b;
+    g = a;
+    h = b;
+}
+int r = g+h;
+return p-r;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testStruct() {
+        CodeGen code = new CodeGen("""
+struct Bar {
+    int a;
+    int b;
+};
+struct Foo {
+    int x;
+};
+Foo? foo = null;
+Bar !bar = new Bar;
+bar.a = 1;
+bar.a = 2;
+return bar.a;
+""");
+        code.parse().opto();
+        assertEquals("return 2;", code.print());
+    }
+
+    @Test
+    public void testExample() {
+        CodeGen code = new CodeGen("""
+struct Vector2D { int x; int y; };
+Vector2D !v = new Vector2D;
+v.x = 1;
+if (arg)
+    v.y = 2;
+else
+    v.y = 3;
+return v;
+""");
+        code.parse().opto();
+        assertEquals("return Vector2D;", code.print());
+    }
+
+    @Test
+    public void testBug() {
+        CodeGen code = new CodeGen("""
+struct s0 {
+    int v0;
+};
+s0? v1=null;
+int v3=v1.zAicm;
+""");
+        try { code.parse();  fail(); }
+        catch( Exception e ) {  assertEquals("Accessing unknown field 'zAicm' from 'null'",e.getMessage());  }
+    }
+
+    @Test
+    public void testBug2() {
+        CodeGen code = new CodeGen("""
+struct s0 { int v0; };
+arg=0+new s0.0;
+""");
+        try { code.parse(); fail(); }
+        catch( Exception e ) { assertEquals("Expected an identifier, found 'null'",e.getMessage()); }
+    }
+
+    @Test
+    public void testLoop() {
+        CodeGen code = new CodeGen("""
+struct Bar { int a; };
+Bar !bar = new Bar;
+while (arg) {
+    bar.a = bar.a + 2;
+    arg = arg + 1;
+}
+return bar.a;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_a+2));", code.print());
+    }
+
+    @Test
+    public void testIf() {
+        CodeGen code = new CodeGen("""
+struct Bar { int a; };
+Bar !bar = new Bar;
+if (arg) bar = null;
+bar.a = 1;
+return bar.a;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type null is not of declared type *Bar",e.getMessage()); }
+    }
+
+    @Test
+    public void testIf2() {
+        CodeGen code = new CodeGen("""
+struct Bar { int a; };
+Bar? !bar = null;
+if (arg) bar = new Bar;
+bar.a = 1;
+return bar.a;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Might be null accessing 'a'",e.getMessage()); }
+    }
+
+    @Test
+    public void testIf3() {
+        CodeGen code = new CodeGen("""
+struct Bar { int a; };
+Bar bar = null;
+if (arg) bar = null;
+bar.a = 1;
+return bar.a;
+""");
+        try { code.parse(); fail(); }
+        catch( Exception e ) { assertEquals("Type null is not of declared type *Bar", e.getMessage()); }
+    }
+
+    @Test
+    public void testIfOrNull() {
+        CodeGen code = new CodeGen("""
+struct Bar { int a; };
+Bar? !bar = new Bar;
+if (arg) bar = null;
+if( bar ) bar.a = 1;
+return bar;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,null,Bar);", code.print());
+    }
+
+    @Test
+    public void testIfOrNull2() {
+        CodeGen code = new CodeGen(
+"""
+struct Bar { int a; };
+Bar? !bar = new Bar;
+if (arg) bar = null;
+int rez = 3;
+if( !bar ) rez=4;
+else bar.a = 1;
+return rez;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,4,3);", code.print());
+    }
+
+    @Test
+    public void testWhileWithNullInside() {
+        CodeGen code = new CodeGen("""
+struct s0 {int v0;};
+s0? !v0 = new s0;
+int ret = 0;
+while(arg) {
+    ret = v0.v0;
+    v0 = null;
+    arg = arg - 1;
+}
+return ret;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) {
+            assertEquals("Might be null accessing 'v0'", e.getMessage()); }
+    }
+
+    @Test
+    public void testRedeclareStruct() {
+        CodeGen code = new CodeGen("""
+struct s0 {
+    int v0;
+};
+s0? v1=new s0;
+s0? v1;
+v1=new s0;
+""");
+        try { code.parse(); fail(); }
+        catch( Exception e ) { assertEquals("Redefining name 'v1'", e.getMessage()); }
+    }
+
+    @Test
+    public void testIter() {
+        // Build and use an iterator
+        CodeGen code = new CodeGen(
+"""
+struct Iter {
+    int x;
+    int len;
+};
+Iter !i = new Iter;
+i.len = arg;
+int sum=0;
+while( i.x < i.len ) {
+    sum = sum + i.x;
+    i.x = i.x + 1;
+}
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi(Loop,0,(Phi_x+1))+Phi_sum));", code.print());
+    }
+
+
+    @Test
+    public void test1() {
+        CodeGen code = new CodeGen("""
+struct s0 {int v0;};
+s0 !ret = new s0;
+while(arg) {
+    s0 !v0 = new s0;
+    v0.v0 = arg;
+    arg = arg-1;
+    if (arg==5) ret=v0;
+
+}
+return ret;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,s0,Phi(Region,s0,Phi_ret));", code.print());
+    }
+
+    @Test
+    public void test2() {
+        CodeGen code = new CodeGen("""
+struct s0 {int v0;};
+s0 !ret = new s0;
+s0 !v0 = new s0;
+while(arg) {
+    v0.v0 = arg;
+    arg = arg-1;
+    if (arg==5) ret=v0;
+
+}
+return ret;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,s0,Phi(Region,s0,Phi_ret));", code.print());
+    }
+
+
+    @Test
+    public void test3() {
+        CodeGen code = new CodeGen("""
+struct s0 {int v0;};
+s0 !ret = new s0;
+while(arg < 10) {
+    s0 !v0 = new s0;
+    if (arg == 5) ret=v0;
+    arg = arg + 1;
+}
+return ret;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,s0,Phi(Region,s0,Phi_ret));", code.print());
+    }
+
+    @Test
+    public void testBug3() {
+        CodeGen code = new CodeGen("""
+struct s0 { int f0; };
+return new s0;
+int v0=null.f0;
+""");
+        try { code.parse();  fail(); }
+        catch( Exception e ) {  assertEquals("Accessing unknown field 'f0' from 'null'",e.getMessage());  }
+    }
+
+    @Test
+    public void testBug4() {
+        CodeGen code = new CodeGen("""
+if(0) {
+    while(0) if(arg) continue;
+    int v0=0;
+    while(1) {
+        int v2=-arg;
+        v0=v2;
+    }
+}
+   """);
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testBug5() {
+        CodeGen code = new CodeGen("""
+struct s0 {
+    int f0;
+};
+if(0) return 0;
+else return new s0;
+if(new s0.f0) return 0;
+    """);
+        code.parse().opto();
+        assertEquals("return s0;", code.print());
+    }
+
+    @Test
+    public void testBug6MissedWorklist() {
+        CodeGen code = new CodeGen("""
+while(0) {}
+int v4=0;
+while(0<arg) {
+    v4=v4+1;
+    while(1) v4=-v4;
+    while(0) arg=-1;
+}
+return 0;
+    """);
+        code.parse().opto();
+    }
+
+    @Test
+    public void testBug7() {
+        CodeGen code = new CodeGen("""
+struct s0 {  int f0; };
+s0 v0 = new s0;
+while(v0.f0) {}
+s0 v1 = v0;
+return v1;
+    """);
+        code.parse().opto();
+        assertEquals("return (const)s0;", code.print());
+    }
+
+
+    @Test
+    public void testBug8() {
+        CodeGen code = new CodeGen("""
+int v2=0;
+while(0)
+while(0) {}
+{
+    {
+        {
+            int v36=0;
+            {
+                while(0) {
+                    {
+                        while(-v2) {
+                            {
+                                while(v36) {
+                                                while(v2) return 0;
+                                                break;
+                                }                            }
+                            if(-v2) break;
+                        }
+                    }
+                }
+            }
+        }    }
+}
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testBug9() {
+        CodeGen code = new CodeGen("""
+int v0=arg==0;
+while(v0) continue;
+return 0;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter11Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter11Test.java
new file mode 100644
index 00000000..0b24bd5d
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter11Test.java
@@ -0,0 +1,552 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+
+
+import static org.junit.Assert.assertEquals;
+
+public class Chapter11Test {
+
+    // A placeholder test used to rapidly rotate through fuzzer produced issues
+    @Test
+    public void testFuzzer() {
+        CodeGen code = new CodeGen(
+"""
+while(---- -arg) {
+    while(-arg) {
+        while(-----arg*---0) {
+                int N=--false==false<--arg;
+                while(N<-4==N) {
+                    N=N+N;
+                }
+            }
+        {
+            int kzEl_r7EYz=3*----0!=-arg<(37*--97!=0/arg==arg)<=-(--arg!=0);
+            while(kzEl_r7EYz<---1) {
+                kzEl_r7EYz=kzEl_r7EYz+kzEl_r7EYz*arg>=24;
+                if(7) continue;
+                kzEl_r7EYz=false;
+                if(-kzEl_r7EYz+arg<-3) continue;
+                else {
+                    while(kzEl_r7EYz) continue;
+                    arg=----3;
+                    kzEl_r7EYz=-(-----arg*1>-kzEl_r7EYz);
+                    int v2uF_4ba=9;
+                }
+            }
+        }
+        int pjcp7rv=arg;
+        {
+            int m2ya3=--arg-pjcp7rv;
+            while(m2ya3<-----pjcp7rv>=pjcp7rv+--pjcp7rv!=---pjcp7rv!=-arg<---(-m2ya3)>m2ya3<=-----true>14!=--m2ya3) {
+                m2ya3=m2ya3+-(--0<=false<pjcp7rv/arg<=-true);
+                while((--m2ya3)<--arg<-----arg*false!=arg<pjcp7rv*arg) {
+                    pjcp7rv=-3+-arg;
+                    break;
+                }
+                while(-3) {
+                    while(67+0-61) m2ya3=m2ya3;
+                    if(----pjcp7rv==---(---arg)) pjcp7rv=0!=-23;
+                    else pjcp7rv=----89;
+                    while(m2ya3!=m2ya3<pjcp7rv) m2ya3=1;
+                    while(--arg<=pjcp7rv) pjcp7rv=-32<=-m2ya3+62;
+                }
+                break;
+            }
+        }
+        {
+            int arg=-1<-9!=(-arg>=-pjcp7rv>=arg<=arg);
+            while(arg<-arg) {
+                arg=arg+--arg;
+                {
+                    while((--93)--pjcp7rv*-pjcp7rv+arg) arg=0-(6>=(--(---41/(0))!=--pjcp7rv)>=---2*33);
+                    pjcp7rv=11;
+                    int c=pjcp7rv;
+                    if(--107) break;
+                    else break;
+                }
+            }
+        }
+        pjcp7rv=pjcp7rv;
+        int aR0Wkua=-pjcp7rv==pjcp7rv;
+        {
+            if(-0!=-0) while(-true) break;
+            else {
+                while(aR0Wkua) pjcp7rv=-0/pjcp7rv;
+                pjcp7rv=pjcp7rv;
+            }
+        }
+    }
+    if(-arg) {
+        {
+            int Isdlt0fr91=0!=arg;
+            while(Isdlt0fr91<-Isdlt0fr91==-Isdlt0fr91+true) {
+                Isdlt0fr91=Isdlt0fr91+-1!=true;
+                if(-arg) if(--arg<=Isdlt0fr91) Isdlt0fr91=-Isdlt0fr91;
+                int i=---arg<---arg!=--40;
+                {
+                    int jVX43Ln4Dm=-(6)==-Isdlt0fr91/----0;
+                    while(jVX43Ln4Dm<--(3-3)) {
+                        jVX43Ln4Dm=jVX43Ln4Dm+-0<25;
+                        i=24<--(jVX43Ln4Dm);
+                    }
+                }
+                i=(arg!=----false>=7);
+                int Te=5>-arg;
+                break;
+            }
+        }
+        arg=arg!=--true/arg;
+        {
+            int UX=arg;
+            while(UX<-3*arg) {
+                UX=UX+arg/-1;
+                arg=-3--(-UX- -47<arg==--arg==arg)/arg- -UX>=-arg;
+                if(---12) while(-UX) break;
+                break;
+            }
+        }
+        continue;
+    }
+    if(arg) arg=--0;
+    else if(1) continue;
+    int DtTlhjYq=19==arg;
+    {
+        arg=--DtTlhjYq<=(DtTlhjYq/---DtTlhjYq<=-DtTlhjYq);
+        if(---arg) continue;
+        else {
+                int Zsl=40;
+                while(Zsl<--Zsl--false>((Zsl))==Zsl!=--DtTlhjYq-DtTlhjYq-DtTlhjYq) {
+                    Zsl=Zsl+arg;
+                }
+            }
+        if((arg)) if(-DtTlhjYq) {
+            }
+            else while(((2)==3*arg/DtTlhjYq)<=0==---arg) return false;
+        else {
+                int lwbF=arg>=0;
+                while(lwbF<57) {
+                    lwbF=lwbF+--(-arg+lwbF)>=-2>=arg!=arg;
+                    arg=----0+0;
+                    while(49) break;
+                    if(true) DtTlhjYq=-----arg;
+                    DtTlhjYq=0!=-----(0);
+                }
+            }
+        arg=---arg!=DtTlhjYq/--0;
+        DtTlhjYq=-DtTlhjYq/(--arg<arg);
+        if(32) {
+                int q=-DtTlhjYq;
+                while(q<arg*(0*q)/0) {
+                    q=q+DtTlhjYq;
+                    DtTlhjYq=arg;
+                }
+            }
+        else if(--arg) if(15) break;
+                else arg=0==arg<=-55>DtTlhjYq;
+            else {
+            }
+        DtTlhjYq=-0;
+        {
+            while((0)<-arg) DtTlhjYq=-DtTlhjYq;
+        }
+        if(30/--(arg)>=0) DtTlhjYq=-0>=arg;
+        else {
+            int Y2wcIQJ=--DtTlhjYq*---11;
+            if(arg==arg) {
+                Y2wcIQJ=-----Y2wcIQJ;
+                Y2wcIQJ=Y2wcIQJ<7;
+                if(DtTlhjYq) arg=arg;
+                else break;
+                while(-arg!=-31==(false<=-15>=-DtTlhjYq+--6*-----Y2wcIQJ<=---arg!=-Y2wcIQJ<=---0<-arg*--Y2wcIQJ)) DtTlhjYq=arg!=3;
+            }
+            continue;
+        }
+        arg=DtTlhjYq;
+        arg=--3/(---arg)>=80>=-DtTlhjYq<=DtTlhjYq;
+        arg=51+---(-true)!=arg!=----1==-DtTlhjYq;
+        if(11<=arg) if((arg)+79<32+(-arg)) continue;
+            else if(true==DtTlhjYq) break;
+        break;
+    }
+}
+if(arg!=62==arg) {
+    while(---arg) {
+        {
+            int bhmDacPM=arg/arg;
+            while(bhmDacPM<arg) {
+                bhmDacPM=bhmDacPM+80*((-bhmDacPM)/---bhmDacPM>1)<bhmDacPM-2!=7;
+                arg=-0;
+                arg=bhmDacPM>=-arg+-arg;
+                break;
+            }
+        }
+        int arg=true;
+        arg=arg<=arg;
+        {
+            int KlC=30;
+            while(KlC<-2) {
+                KlC=KlC+-1!=25<=-KlC>KlC>----0;
+                int Ij=arg>=-arg<=---10;
+                {
+                    int LAbgurVa2R=-arg!=Ij;
+                    while(LAbgurVa2R<-true) {
+                        LAbgurVa2R=LAbgurVa2R+Ij;
+                        KlC=-LAbgurVa2R;
+                        Ij=42*(-Ij>true);
+                        while(Ij) arg=KlC;
+                        KlC=-----7>-(--KlC<--7)==-LAbgurVa2R;
+                    }
+                }
+                int a=Ij<=-KlC;
+                if(Ij) {
+                    int r1W=a!=-false;
+                }
+                else {
+                    arg=56>=Ij;
+                    while(54) break;
+                    arg=8>=-(a<--Ij)/a>=-a-KlC;
+                }
+                int Yt_T=KlC;
+                arg=KlC;
+            }
+        }
+        if(----false/--arg/12+-----0) if(-9+-arg) while(arg!=(arg)) arg=--1>=-71-arg!=---(--arg*11+102)/--arg;
+            else if(----arg) continue;
+        if(-arg-arg) {
+            arg=-(-arg)*--(-3)<(-7==-arg----arg);
+            {
+                int arg=arg;
+                while(arg<-0>arg==-arg-(-arg>1+11)) {
+                    arg=arg+6-arg!=--0>---30>=---arg<=arg/(3)+---arg;
+                }
+            }
+            arg=-arg+arg;
+            arg=--47+-arg<1>arg*(-arg==-arg- -0>3);
+            arg=(----arg)!=arg+--59;
+            arg=- -4+arg==-(arg)-arg;
+        }
+        else {
+            while(--true-----true*-25+-18>arg>=-----(-arg)---13) {
+                arg=-0+--true<false;
+                continue;
+            }
+            arg=true<=arg;
+            break;
+        }
+        arg=arg*22<--(0+-arg);
+        {
+            continue;
+        }
+    }
+    arg=1*---((3<=true)==---2);
+    arg=7+-(-1);
+    return arg+--true;
+}
+else {
+    int o3ypEsewxM=-(---arg);
+    int vzXB=(-(---11<=--o3ypEsewxM>=--0))<=-0/-arg;
+    int L=-arg;
+    int B4mHcrf=---vzXB;
+    int oZWGdzZl=-o3ypEsewxM;
+    int K6tQqa1=11;
+    while(0!=--L) {
+            int sdZfTM=vzXB*true+K6tQqa1;
+            while(sdZfTM<false) {
+                sdZfTM=sdZfTM+arg;
+                sdZfTM=oZWGdzZl;
+                K6tQqa1=-K6tQqa1;
+                arg=---K6tQqa1;
+                while((3+-K6tQqa1)<oZWGdzZl) {
+                    if(-----(-1)) sdZfTM=-false;
+                    {}
+                }
+                K6tQqa1=vzXB!=-(B4mHcrf+-7>false);
+                sdZfTM=vzXB;
+            }
+        }
+    L=false;
+    while(31) B4mHcrf=arg;
+    oZWGdzZl=-0<--oZWGdzZl<=--2;
+    if(K6tQqa1>=20<=46) {
+        if(-1+-L) if(oZWGdzZl) {
+                int wmhv=-----0;
+            }
+        int arg=0;
+        o3ypEsewxM=---(oZWGdzZl);
+        return -oZWGdzZl/0;
+    }
+    else if(arg) {
+            int yKk5=B4mHcrf>=4>K6tQqa1<-B4mHcrf/o3ypEsewxM;
+            return -K6tQqa1;
+        }
+        else {
+            if(---0) {
+                {}
+                {}
+            }
+            return o3ypEsewxM;
+        }
+}
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return Phi(Region,9,Top,Top,Top,Top);", code.print());
+    }
+
+
+    @Test
+    public void testPrimes() {
+        CodeGen code = new CodeGen(
+"""
+if( arg < 2 ) return 0;
+int primeCount = 1;
+int prime = 3;
+while( prime <= arg ) {
+    int isPrime = 1;
+    // Check for even case, so the next loop need only check odds
+    if( (prime/2)*2 == prime )
+        continue;
+    // Check odds up to sqrt of prime
+    int j = 3;
+    while( j*j <= prime ) {
+        if( (prime/j)*j == prime ) {
+            isPrime = 0;
+            break;
+        }
+        j = j + 2;
+    }
+    if( isPrime )
+        primeCount = primeCount + 1;
+    prime = prime + 2;
+}
+return primeCount;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,Phi(Loop,1,Phi(Region,Phi_primeCount,Phi(Region,(Phi_primeCount+1),Phi_primeCount))));", code.print());
+        assertEquals("0", Eval2.eval(code,  1)); // No primes 1 or below
+        assertEquals("1", Eval2.eval(code,  2)); // 2
+        assertEquals("2", Eval2.eval(code,  3)); // 2, 3
+        assertEquals("2", Eval2.eval(code,  4)); // 2, 3
+        assertEquals("3", Eval2.eval(code,  5)); // 2, 3, 5
+        assertEquals("4", Eval2.eval(code, 10)); // 2, 3, 5, 7
+    }
+
+    @Test
+    public void testAntiDeps1() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v=new S;
+v.f = 2;
+int i=new S.f;
+i=v.f;
+if (arg) v.f=1;
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return 2;", code.print());
+        assertEquals("2", Eval2.eval(code, 0));
+        assertEquals("2", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testAntiDeps2() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+v.f = arg;
+S !t = new S;
+int i = 0;
+if (arg) {
+    if (arg+1) v = t;
+    i = v.f;
+} else {
+    v.f = 2;
+}
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,.f,0);", code.print());
+    }
+
+    @Test
+    public void testAntiDeps3() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v0 = new S;
+S? v1;
+if (arg) v1 = new S;
+if (v1) {
+    v0.f = v1.f;
+} else {
+    v0.f = 2;
+}
+return v0;
+""");
+        code.parse().opto();
+        assertEquals("return S;", code.print());
+    }
+
+
+    @Test
+    public void testAntiDeps4() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+v.f = arg;
+S t = new S;
+int i = v.f;
+if (arg+1) arg= 0;
+while (arg) v.f = 2;
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return arg;", code.print());
+    }
+
+    @Test
+    public void testAntiDeps5() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+while(1) {
+    while(arg+1) { arg=arg-1; }
+    if (arg) break;
+    v.f = 2;
+}
+return v;
+""");
+        code.parse().opto();
+        assertEquals("return S;", code.print());
+    }
+
+    @Test
+    public void testAntiDeps6() {
+        CodeGen code = new CodeGen(
+"""
+struct s { int v; };
+s !ptr=new s;
+while( -arg )
+  ptr = new s;
+while(1)
+  arg = arg+ptr.v;
+""");
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+    @Test
+    public void testAntiDeps7() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+S t = new S;
+int i = v.f;
+while (arg) {
+    v.f = arg;
+    arg = arg-1;
+}
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testAntiDeps8() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+S t = new S;
+while(arg) {
+    arg=arg-1;
+    int f = v.f;
+    v.f = 2;
+    if (arg) arg = f;
+    else v.f = 3;
+}
+return arg;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testAntiDeps9() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+S t = new S;
+if (arg) {
+    v.f=2;
+    int i=t.f;
+    v.f=i;
+}
+return v;
+""");
+        code.parse().opto();
+        assertEquals("return S;", code.print());
+    }
+
+    @Test
+    public void testExample2() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int f; };
+S !v = new S;
+int i = arg;
+while (arg > 0) {
+    int j = i/3;
+    if (arg == 5)
+        v.f = j;
+    arg = arg - 1;
+}
+return v;
+                """);
+        code.parse().opto();
+        //assertEquals("return new S;", code.print());
+    }
+
+    @Test
+    public void testScheduleUse() {
+        CodeGen code = new CodeGen(
+"""
+int v0=0;
+while(0>=0) {
+    u1 v1=0;
+    v1=v0;
+    if(v1*0)
+        v0=-v1;
+}
+return 0;
+""");
+        code.parse().opto();
+        assertEquals("return Top;", code.print());
+    }
+
+    @Test
+    public void testLoopCarriedDep() {
+        CodeGen code = new CodeGen(
+"""
+u32 v0=0;
+{
+    int v1=0;
+    while(v1) {
+        v1=1>>>v0!=0;
+        v0=v1/0;
+    }
+    return v1;
+}
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter12Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter12Test.java
new file mode 100644
index 00000000..21df8205
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter12Test.java
@@ -0,0 +1,62 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Ignore;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter12Test {
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testFloat() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testSquareRoot() {
+        CodeGen code = new CodeGen(
+"""
+flt guess = arg;
+while( 1 ) {
+    flt next = (arg/guess + guess)/2;
+    if( next == guess ) break;
+    guess = next;
+}
+return guess;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,(flt)arg,(((ToFloat/Phi_guess)+Phi_guess)/2.0f));", code.print());
+        assertEquals("3.0", Eval2.eval(code,  9));
+        assertEquals("1.414213562373095", Eval2.eval(code,  2));
+    }
+
+    @Test
+    public void testFPOps() {
+        CodeGen code = new CodeGen(
+"""
+flt x = arg;
+return x+1==x;
+""");
+        code.parse().opto();
+        assertEquals("return ((flt)arg==(ToFloat+1.0f));", code.print());
+        assertEquals("0", Eval2.eval(code, 1));
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter13Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter13Test.java
new file mode 100644
index 00000000..d05fd7d8
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter13Test.java
@@ -0,0 +1,247 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter13Test {
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testLinkedList0() {
+        CodeGen code = new CodeGen(
+"""
+struct LLI { LLI? next; int i; };
+LLI? !head = null;
+while( arg ) {
+    LLI !x = new LLI;
+    x.next = head;
+    x.i = arg;
+    head = x;
+    arg = arg-1;
+}
+return head.next.i;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Might be null accessing 'i'",e.getMessage()); }
+    }
+
+    @Test
+    public void testLinkedList1() {
+        CodeGen code = new CodeGen(
+"""
+struct LLI { LLI? next; int i; };
+LLI? !head = null;
+while( arg ) {
+    LLI !x = new LLI;
+    x.next = head;
+    x.i = arg;
+    head = x;
+    arg = arg-1;
+}
+if( !head ) return 0;
+LLI? next = head.next;
+if( next==null ) return 1;
+return next.i;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,1,.i);", code.print());
+        assertEquals("2", Eval2.eval(code,  3));
+    }
+
+    @Test
+    public void testCoRecur() {
+        CodeGen code = new CodeGen(
+"""
+struct int0 { int i; flt0? f; };
+struct flt0 { flt f; int0? i; };
+int0 !i0 = new int0;
+i0.i = 17;
+flt0 !f0 = new flt0;
+f0.f = 3.14;
+i0.f = f0;
+f0.i = i0;
+return f0.i.f.i.i;
+""");
+        code.parse().opto();
+        assertEquals("return 17;", code.print());
+    }
+
+    @Test
+    public void testNullRef0() {
+        CodeGen code = new CodeGen(
+"""
+struct N { N? next; int i; };
+N n = new N;
+return n.next;
+""");
+        code.parse().opto();
+        assertEquals("return null;", code.print());
+    }
+
+    @Test
+    public void testNullRef1() {
+        CodeGen code = new CodeGen(
+"""
+struct M { int m; };
+struct N { M next; int i; };
+N n = new N { next = new M; };
+return n.next;
+""");
+        code.parse().opto();
+        assertEquals("return (const)M;", code.print());
+    }
+
+    @Test
+    public void testNullRef2() {
+        CodeGen code = new CodeGen(
+"""
+struct M { int m; };
+struct N { M next; int i; };
+N n = new N { next = null; }
+return n.next;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type null is not of declared type *M",e.getMessage()); }
+    }
+
+    @Test
+    public void testNullRef3() {
+        CodeGen code = new CodeGen(
+"""
+struct N { N? next; int i; };
+N !n = new N;
+n.i = 3.14;
+return n.i;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type 3.14 is not of declared type int",e.getMessage()); }
+    }
+
+    @Test
+    public void testEmpty() {
+        CodeGen code = new CodeGen(
+"""
+struct S{};
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testForwardRef0() {
+        CodeGen code = new CodeGen(
+"""
+struct S1 { S2? s; };
+return new S2;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Unknown struct type 'S2'",e.getMessage()); }
+    }
+
+    @Test
+    public void testForwardRef1() {
+        CodeGen code = new CodeGen(
+"""
+struct S1 { S2? s; };
+struct S2 { int x; };
+return new S1.s=new S2;
+""");
+        code.parse().opto();
+        assertEquals("return S2;", code.print());
+    }
+
+    @Test
+    public void testcheckNull() {
+        CodeGen code = new CodeGen(
+"""
+struct I {int i;};
+struct P { I? pi; };
+P !p1 = new P;
+P !p2 = new P;
+p2.pi = new I;
+p2.pi.i = 2;
+if (arg) p1 = new P;
+return p1.pi.i + 1;
+""");
+        try { code.parse().opto().typeCheck();  fail(); }
+        catch( Exception e ) {  assertEquals("Might be null accessing 'i'",e.getMessage());  }
+    }
+
+    @Test
+    public void testCoRecur2() {
+        CodeGen code = new CodeGen(
+"""
+struct A { L? a; T? b; F? c; };  A? !a = new A;
+struct B { M? a; U? b; G? c; };  B? !b = new B;
+struct C { N? a; V? b; H? c; };  C? !c = new C;
+struct D { O? a; W? b; I? c; };  D? !d = new D;
+struct E { P? a; X? b; J? c; };  E? !e = new E;
+struct F { Q? a; Y? b; K? c; };  F? !f = new F;
+struct G { R? a; Z? b; L? c; };  G? !g = new G;
+struct H { S? a; A? b; M? c; };  H? !h = new H;
+struct I { T? a; B? b; N? c; };  I? !i = new I;
+struct J { U? a; C? b; O? c; };  J? !j = new J;
+struct K { V? a; D? b; P? c; };  K? !k = new K;
+struct L { W? a; E? b; Q? c; };  L? !l = new L;
+struct M { X? a; F? b; R? c; };  M? !m = new M;
+struct N { Y? a; G? b; S? c; };  N? !n = new N;
+struct O { Z? a; H? b; T? c; };  O? !o = new O;
+struct P { A? a; I? b; U? c; };  P? !p = new P;
+struct Q { B? a; J? b; V? c; };  Q? !q = new Q;
+struct R { C? a; K? b; W? c; };  R? !r = new R;
+struct S { D? a; L? b; X? c; };  S? !s = new S;
+struct T { E? a; M? b; Y? c; };  T? !t = new T;
+struct U { F? a; N? b; Z? c; };  U? !u = new U;
+struct V { G? a; O? b; A? c; };  V? !v = new V;
+struct W { H? a; P? b; B? c; };  W? !w = new W;
+struct X { I? a; Q? b; C? c; };  X? !x = new X;
+struct Y { J? a; R? b; D? c; };  Y? !y = new Y;
+struct Z { K? a; S? b; E? c; };  Z? !z = new Z;
+
+a.a=l;  a.b=t; a.c=f;
+b.a=m;  b.b=u; b.c=g;
+c.a=n;  c.b=v; c.c=h;
+d.a=o;  d.b=w; d.c=i;
+e.a=p;  e.b=x; e.c=j;
+f.a=q;  f.b=y; f.c=k;
+g.a=r;  g.b=z; g.c=l;
+h.a=s;  h.b=a; h.c=m;
+i.a=t;  i.b=b; i.c=n;
+j.a=u;  j.b=c; j.c=o;
+k.a=v;  k.b=d; k.c=p;
+l.a=w;  l.b=e; l.c=q;
+m.a=x;  m.b=f; m.c=r;
+n.a=y;  n.b=g; n.c=s;
+o.a=z;  o.b=h; o.c=t;
+p.a=a;  p.b=i; p.c=u;
+q.a=b;  q.b=j; q.c=v;
+r.a=c;  r.b=k; r.c=w;
+s.a=d;  s.b=l; s.c=x;
+t.a=e;  t.b=m; t.c=y;
+u.a=f;  u.b=n; u.c=z;
+v.a=g;  v.b=o; v.c=a;
+w.a=h;  w.b=p; w.c=b;
+x.a=i;  x.b=q; x.c=c;
+y.a=j;  y.b=r; y.c=d;
+z.a=k;  z.b=s; z.c=e;
+
+return a.b.c.a.b.c.a.b.c.a.b.c.a.b.c.a.b.c;
+
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return R;", code._stop.toString());
+        assertEquals("R{a=C{a=N{a=Y{a=J{a=U{a=F{a=Q{a=B{a=M{a=X{a=I{a=T{a=E{a=P{a=A{a=L{a=W{a=H{a=S{a=D{a=O{a=Z{a=K{a=V{a=G{a=$cyclic,b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic},b=$cyclic,c=$cyclic}", Eval2.eval(code,  0));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter14Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter14Test.java
new file mode 100644
index 00000000..17708c37
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter14Test.java
@@ -0,0 +1,226 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter14Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testRange() {
+        CodeGen code = new CodeGen(
+"""
+int b;
+if( arg ) b=1; else b=0;
+int c = 99;
+if( b < 0 ) c = -1;
+if( b > 2 ) c =  1;
+return c;
+""");
+        code.parse().opto();
+        assertEquals("return 99;", code.print());
+        assertEquals("99", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testU8() {
+        CodeGen code = new CodeGen(
+"""
+u8 b = 123;
+b = b + 456;// Truncate
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return 67;", code.print());
+        assertEquals("67", Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testU8While() {
+        CodeGen code = new CodeGen(
+"""
+u8 b = 123;
+while( b ) b = b + 456;// Truncate
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testU1() {
+        CodeGen code = new CodeGen(
+"""
+bool b = 123;
+b = b + 456;// Truncate
+u1 c = b;   // No more truncate needed
+return c;
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testAnd() {
+        CodeGen code = new CodeGen(
+"""
+int b = 123;
+b = b+456 & 31;                 // Precedence
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+        assertEquals("3", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testRefLoad() {
+        CodeGen code = new CodeGen(
+"""
+struct Foo { u1 b; };
+Foo !f = new Foo;
+f.b = 123;
+return f.b;
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testSigned() {
+        CodeGen code = new CodeGen(
+"""
+i8 b = 255;                     // Chopped
+return b;                       // Sign extend
+""");
+        code.parse().opto();
+        assertEquals("return -1;", code.print());
+        assertEquals("-1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testI8() {
+        CodeGen code = new CodeGen(
+"""
+i8 b = arg;
+b = b + 1;// Truncate
+return b;
+""");
+        code.parse().opto();
+        assertEquals("return (((((arg<<56)>>56)+1)<<56)>>56);", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+        assertEquals("-128", Eval2.eval(code, 127));
+    }
+
+    @Test
+    public void testMask() {
+        CodeGen code = new CodeGen(
+"""
+u16 mask = (1<<16)-1;           // AND mask
+int c = 123456789 & mask;
+return c;                       //
+""");
+        code.parse().opto();
+        assertEquals("return 52501;", code.print());
+        assertEquals("52501", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testOr() {
+        CodeGen code = new CodeGen(
+"""
+return (arg | 123 ^ 456) >>> 1;
+""");
+        code.parse().opto();
+        assertEquals("return (((arg|123)^456)>>>1);", code.print());
+        assertEquals("217", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testMaskFloat() {
+        CodeGen code = new CodeGen(
+"""
+flt f = arg;
+arg = f & 1;
+return arg;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot '&' flt",e.getMessage()); }
+    }
+
+    @Test
+    public void testCloneAnd() {
+        CodeGen code = new CodeGen("""
+int v0=0;
+u32 v1 = 1&(1<<arg)&(1<<arg);
+while(arg) v1=-v0;
+while(v1) break;
+return v1;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,(((1<<arg)&1)&Shl),0);", code.print());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testAndHigh() {
+        CodeGen code = new CodeGen("""
+int v0=0;
+if(0&0>>>0) {
+    while(0) {
+        u8 v1=0;
+        v0=0>>>0;
+        v1=arg;
+        while(v1+0) {}
+    }
+}
+return v0;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testTypes() {
+        CodeGen code = new CodeGen(
+"""
+i8  xi8  = 123456789;  if( xi8  !=        21 ) return -8;
+i16 xi16 = 123456789;  if( xi16 !=    -13035 ) return -16;
+i32 xi32 = 123456789;  if( xi32 != 123456789 ) return -32;
+i64 xi64 = 123456789;  if( xi64 != 123456789 ) return -64;
+int xint = 123456789;  if( xint != 123456789 ) return -64;
+
+u1  ui1  = 123456789;  if( ui1  !=         1 ) return 1;
+u8  ui8  = 123456789;  if( ui8  !=        21 ) return 8;
+u16 ui16 = 123456789;  if( ui16 !=     52501 ) return 16;
+u32 ui32 = 123456789;  if( ui32 != 123456789 ) return 32;
+
+flt fflt = 3.141592653589793;  if( fflt != 3.141592653589793 ) return 3;
+f64 ff64 = 3.141592653589793;  if( ff64 != 3.141592653589793 ) return 3;
+f32 ff32 = 3.141592653589793;  if( ff32 != 3.1415927410125732) return 5;
+
+return 0;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter15Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter15Test.java
new file mode 100644
index 00000000..546eb0e9
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter15Test.java
@@ -0,0 +1,380 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class Chapter15Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testCyclic() {
+        CodeGen code = new CodeGen(
+"""
+struct C { C? l; };
+C !c = new C;
+c.l = c;
+return c;
+""");
+        code.parse().opto();
+        assertEquals("return C;", code.print());
+        assertEquals("C{l=$cyclic}", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testSafetyCheck() {
+        CodeGen code = new CodeGen(
+"""
+u8[] old = new u8[0];
+u8[] !output = new u8[1];
+int i = 0;
+while (i < old#) {
+    output[i] = old[i];
+    i = i + 1;
+}
+output[i] = 1;
+return output;
+""");
+        code.parse().opto();
+        assertEquals("return [u8];", code.print());
+        assertEquals("\u0001", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testBasic1() {
+        CodeGen code = new CodeGen(
+"""
+int[] is = new int[2];
+return is[1];
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testBasic2() {
+        CodeGen code = new CodeGen(
+"""
+int[] is = new int[2];
+int[] is2 = new int[2];
+return is[1];
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testBasic3() {
+        CodeGen code = new CodeGen(
+"""
+int[] !a = new int[2];
+a[0] = 1;
+a[1] = 2;
+return a[0];
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testBasic4() {
+        CodeGen code = new CodeGen(
+"""
+struct A { int i; };
+A?[] !a = new A?[2];
+return a;
+""");
+        code.parse().opto();
+        assertEquals("return [*A?];", code.print());
+        assertEquals("*A {int !i; }?[ null,null]", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testBasic5() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int x; flt y; };
+// A new S
+S !s = new S; s.x=99; s.y = 3.14;
+
+// Double-d array of Ss.  Fill in one row.
+S?[]?[] !iss = new S?[]?[2];
+iss[0] = new S?[7];
+iss[0][2] = s;
+
+// Now pull out the filled-in value, with null checks
+flt rez;
+S?[]? is = iss[arg];
+if( !is ) rez = 1.2;
+else {
+    S? i = is[2];
+    if( !i ) rez = 2.3;
+    else rez = i.y;
+}
+return rez;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,1.2,Phi(Region,2.3,.y));", code.print());
+        assertEquals("3.14", Eval2.eval(code, 0));
+        assertEquals("1.2", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testBasic6() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int x; flt y; };
+// A new S
+S !s = new S; s.x=99; s.y = 3.14;
+
+// Double-d array of Ss.  Fill in one row.
+S?[]?[] !iss = new S?[]?[2];
+iss[0] = new S?[7];
+iss[0][2] = s;
+
+// Now pull out the filled-in value, with null checks
+flt rez = 1.2;
+if( iss[arg] )
+    if( iss[arg][2] )
+        rez = iss[arg][2].y;
+return rez;""");
+        code.parse().opto().typeCheck();
+        assertEquals("return Phi(Region,Phi(Region,.y,1.2),1.2);", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+        try { Eval2.eval(code, 10); fail(); } // Fails AIOOBE in Eval2, no range checks
+        catch( Exception e ) { assertEquals("Index 10 out of bounds for length 2",e.getMessage()); }
+    }
+
+    @Test
+    public void testTree() {
+        CodeGen code = new CodeGen(
+"""
+// Can we define a forward-reference array?
+struct Tree { Tree?[]? _kids; };
+Tree !root = new Tree;
+root._kids = new Tree?[2]; // NO BANG SO ARRAY IS OF IMMUTABLE TREES????
+root._kids[0] = new Tree;
+return root;
+""");
+        code.parse().opto();
+        assertEquals("return Tree;", code.print());
+        assertEquals("Tree{_kids=*Tree?[ Tree{_kids=null},null]}", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testNestedStructAddMemProj() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int a; int[] b; };
+return 0;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testRollingSum() {
+        CodeGen code = new CodeGen(
+"""
+int[] !ary = new int[arg];
+// Fill [0,1,2,3,4,...]
+int i=0;
+while( i < ary# ) {
+    ary[i] = i;
+    i = i+1;
+}
+// Fill [0,1,3,6,10,...]
+i=0;
+while( i < ary# - 1 ) {
+    ary[i+1] = ary[i+1] + ary[i];
+    i = i+1;
+}
+return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
+""");
+        code.parse().opto();
+        assertEquals("return (.[]+(.[]*1000));", code.print());
+        assertEquals("1006", Eval2.eval(code,  4));
+    }
+
+    @Test
+    public void sieveOEratosthenes() {
+        CodeGen code = new CodeGen(
+"""
+int[] !ary = new int[arg], !primes = new int[arg];
+int nprimes = 0, p=2;
+// Find primes while p^2 < arg
+while( p*p < arg ) {
+    // skip marked non-primes
+    while( ary[p]==1 ) p = p + 1;
+    // p is now a prime
+    primes[nprimes] = p;  nprimes = nprimes + 1;
+    // Mark out the rest non-primes
+    int i = p + p;
+    while( i < ary# ) {
+        ary[i] = 1;
+        i = i + p;
+    }
+    p = p + 1;
+}
+// Now just collect the remaining primes, no more marking
+while( p < arg ) {
+    if( ary[p] == 0 ) {
+        primes[nprimes] = p;  nprimes = nprimes + 1;
+    }
+    p = p + 1;
+}
+// Copy/shrink the result array
+int[] !rez = new int[nprimes];
+int j = 0;
+while( j < nprimes ) {
+    rez[j] = primes[j];
+    j = j + 1;
+}
+return rez;
+""");
+        code.parse().opto();
+        assertEquals("return [int];", code.print());
+        assertEquals("int[ 2,3,5,7,11,13,17,19]",Eval2.eval(code, 20));
+    }
+
+    @Test
+    public void testNewNodeInit() {
+        CodeGen code = new CodeGen(
+"""
+struct S {int i; flt f;};
+S !s1 = new S;
+S !s2 = new S;
+s2.i = 3;
+s2.f = 2.0;
+if (arg) s1 = new S;
+return s1.i + s1.f;
+""");
+        code.parse().opto();
+        assertEquals("return ((flt).i+.f);", code.print());
+        assertEquals("0.0", Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testBad0() {
+        CodeGen code = new CodeGen(
+"""
+return new flt;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot allocate a flt",e.getMessage()); }
+    }
+
+    @Test
+    public void testBad1() {
+        CodeGen code = new CodeGen(
+"""
+int is = new int[2];
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type *[int] is not of declared type int",e.getMessage()); }
+    }
+
+    @Test
+    public void testBad2() {
+        CodeGen code = new CodeGen(
+"""
+int[] is = new int[3.14];
+return is[1];
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot allocate an array with length 3.14",e.getMessage()); }
+    }
+
+    @Test
+    public void testBad3() {
+        CodeGen code = new CodeGen(
+"""
+int[] is = new int[arg];
+return is[1];
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  4));
+        try { Eval2.eval(code,0); }
+        catch( ArrayIndexOutOfBoundsException e ) { assertEquals("Array index 1 out of bounds for array length 0",e.getMessage()); }
+        try { Eval2.eval(code,-1); }
+        catch( NegativeArraySizeException e ) { assertEquals("-1",e.getMessage()); }
+    }
+
+    @Test
+    public void testProgress() {
+        CodeGen code = new CodeGen("""
+i8 v1=0&0;
+u8 v2=0;
+byte v4=0;
+if(0) {}
+while(v2<0) {
+    v4=0-v1;
+    break;
+}
+int v5=0&0;
+while(v5+(0&0)) {
+    int v7=0&0;
+    while(v7)
+        v4=0>>>v5;
+    while(v1)
+        return 0;
+}
+return v1;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testSharpNot() {
+        CodeGen code = new CodeGen(
+"""
+if(0>>0) {}
+while(0) {}
+u32 v7=0;
+int v8=0;
+while(0<--1>>>---(v7*0==v8)) {}
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+
+
+    @Test
+    public void testProgress2() {
+        CodeGen code = new CodeGen(
+"""
+if(1) {}
+else {
+        while(arg>>>0&0>>>0) {}
+    byte v3=0>>>0;
+                while(0) {}
+        int v7=0>>>0;
+        while(v7<0>>>0) {
+                    while(0+v7<=0) if(1) arg=-12;
+            if(arg) {
+                v3=arg+v3+0;
+                arg=0;
+            }
+        }
+}
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter16Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter16Test.java
new file mode 100644
index 00000000..ad3dc690
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter16Test.java
@@ -0,0 +1,260 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter16Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 3.14;
+""");
+        code.parse().opto();
+        assertEquals("return 3.14;", code.print());
+        assertEquals("3.14", Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testMulti0() {
+        CodeGen code = new CodeGen(
+"""
+int x, y;
+return x+y;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+    @Test
+    public void testMulti1() {
+        CodeGen code = new CodeGen(
+"""
+int x=2, y=x+1;
+return x+y;
+""");
+        code.parse().opto();
+        assertEquals("return 5;", code.print());
+        assertEquals("5", Eval2.eval(code,  0));
+    }
+
+//    @Test
+//    public void testFinal0() {
+//        CodeGen code = new CodeGen(
+//"""
+//int !x=2;
+//x=3;
+//return x;
+//""");
+//        try { code.parse().opto(); fail(); }
+//        catch( Exception e ) { assertEquals("Cannot reassign final 'x'",e.getMessage()); }
+//    }
+
+    @Test
+    public void testFinal1() {
+        CodeGen code = new CodeGen(
+"""
+int x=2, y=3;
+if( arg ) { int x = y; x = x*x; y=x; } // Shadow final x
+return y;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,9,3);", code.print());
+        assertEquals("3", Eval2.eval(code, 0));
+        assertEquals("9", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testConstruct0() {
+        CodeGen code = new CodeGen("""
+struct X { int x=3; };
+X z = new X;
+return z.x;
+""");
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+        assertEquals("3", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testConstruct1() {
+        CodeGen code = new CodeGen("""
+struct X { int !x; };
+X z = new X { x=3; };
+return z.x;
+""");
+        code.parse().opto();
+        assertEquals("return 3;", code.print());
+        assertEquals("3", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testConstruct2() {
+        CodeGen code = new CodeGen("""
+struct X { int x=3; };
+X z = new X { x = 4; };
+return z.x;
+""");
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+        assertEquals("4", Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testStructFinal0() {
+        CodeGen code = new CodeGen("""
+struct Point { int !x, !y; };
+Point p = new Point { x=3; y=4; };
+return p;
+""");
+        code.parse().opto();
+        assertEquals("return (const)Point;", code.print());
+        assertEquals("Point{x=3,y=4}", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testStructFinal1() {
+        CodeGen code = new CodeGen("""
+struct Point { int x=3, y=4; };
+Point p = new Point { x=5; y=6; };
+p.x++;
+return p;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal2() {
+        CodeGen code = new CodeGen("""
+struct Point { int x=3, y=4; };
+Point p = new Point;
+p.x++;
+return p;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal3() {
+        CodeGen code = new CodeGen("""
+struct Point { var x; var y; };
+Point p = new Point;
+p.x++;
+return p;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("'Point' is not fully initialized, field 'x' needs to be set in a constructor",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal4() {
+        CodeGen code = new CodeGen("""
+struct Point { val x=3; val y=4; };
+Point p = new Point;
+p.x++;
+return p;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot reassign final 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testStructFinal5() {
+        CodeGen code = new CodeGen("""
+struct Point { var x=3; var y=4; };
+Point !p = new Point;
+p.x++;
+return p;
+""");
+        code.parse().opto();
+        assertEquals("return Point;", code.print());
+        assertEquals("Point{x=4,y=4}", Eval2.eval(code,  0));
+    }
+
+    // Same as the Chapter13 test with the same name, but using the new
+    // constructor syntax
+    @Test
+    public void testLinkedList1() {
+        CodeGen code = new CodeGen(
+"""
+struct LLI { LLI? next; int i; };
+LLI? !head = null;
+while( arg ) {
+    head = new LLI { next=head; i=arg; };
+    arg = arg-1;
+}
+if( !head ) return 0;
+LLI? next = head.next;
+if( !next ) return 1;
+return next.i;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,1,.i);", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+        assertEquals("1", Eval2.eval(code,  1));
+        assertEquals("2", Eval2.eval(code,  3));
+    }
+
+    @Test
+    public void testLinkedList2() {
+        CodeGen code = new CodeGen(
+"""
+struct LLI { LLI? next; int i; };
+LLI? !head = null;
+while( arg ) {
+    head = new LLI {
+        next=head;
+        // Any old code in the constructor
+        int !tmp=arg;
+        while( arg > 10 ) {
+            tmp = tmp + arg;
+            arg = arg - 1;
+        }
+        i=tmp;
+    };
+    arg = arg-1;
+}
+if( !head ) return 0;
+LLI? next = head.next;
+if( !next ) return 1;
+return next.i;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,0,1,.i);", code.print());
+        assertEquals("0", Eval2.eval(code,  0));
+        assertEquals("1", Eval2.eval(code,  1));
+        assertEquals("2", Eval2.eval(code, 11));
+    }
+
+    @Test
+    public void testSquare() {
+        CodeGen code = new CodeGen(
+"""
+struct Square {
+    flt !side = arg;
+    // Newtons approximation to the square root, computed in a constructor.
+    // The actual allocation will copy in this result as the initial
+    // value for 'diag'.
+    flt !diag = arg*arg/2;
+    while( 1 ) {
+        flt next = (side/diag + diag)/2;
+        if( next == diag ) break;
+        diag = next;
+    }
+};
+return new Square;
+""");
+        code.parse().opto();
+        assertEquals("return Square;", code.print());
+        assertEquals("Square{side=3.0,diag=1.7320508075688772}", Eval2.eval(code,  3));
+        assertEquals("Square{side=4.0,diag=2.0}", Eval2.eval(code, 4));
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter17Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter17Test.java
new file mode 100644
index 00000000..a1d0f8b9
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter17Test.java
@@ -0,0 +1,556 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class Chapter17Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+int i = 0;
+i=i=1;
+return i;
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testInc0() {
+        CodeGen code = new CodeGen("""
+return arg++;
+""");
+        code.parse().opto();
+        assertEquals("return arg;", code.print());
+        assertEquals("0", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc1() {
+        CodeGen code = new CodeGen("""
+return arg+++arg++;
+""");
+        code.parse().opto();
+        assertEquals("return ((arg<<1)+1);", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc2() {
+        CodeGen code = new CodeGen("""
+//   -(arg--)-(arg--)
+return -arg---arg--;
+""");
+        code.parse().opto();
+        assertEquals("return (-((arg<<1)+-1));", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc3() {
+        CodeGen code = new CodeGen("""
+int[] !xs = new int[arg];
+xs[0]++;
+xs[1]++;
+return xs[0];
+""");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code, 2));
+    }
+
+    @Test
+    public void testInc4() {
+        CodeGen code = new CodeGen("""
+u8[] !xs = new u8[1];
+xs[0]--;
+return xs[0];
+""");
+        code.parse().opto();
+        assertEquals("return 255;", code.print());
+        assertEquals("255", Eval2.eval(code, 2));
+    }
+
+    @Test
+    public void testInc5() {
+        CodeGen code = new CodeGen("""
+struct S { u16 x; };
+S !s = new S;
+s.x--;
+return s.x;
+""");
+        code.parse().opto();
+        assertEquals("return 65535;", code.print());
+        assertEquals("65535", Eval2.eval(code, 2));
+    }
+
+    @Test
+    public void testInc6() {
+        CodeGen code = new CodeGen("return --arg;");
+        code.parse().opto();
+        assertEquals("return (arg+-1);", code.print());
+        assertEquals("-1", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc7() {
+        CodeGen code = new CodeGen("u8 x=0; return --x;");
+        code.parse().opto();
+        assertEquals("return 255;", code.print());
+        assertEquals("255", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc8() {
+        CodeGen code = new CodeGen("int x; x+=2; return x+=3;");
+        code.parse().opto();
+        assertEquals("return 5;", code.print());
+        assertEquals("5", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testInc9() {
+        CodeGen code = new CodeGen("flt x = 1.5; x++; return x;");
+        code.parse().opto();
+        assertEquals("return 2.5f;", code.print());
+        assertEquals("2.5", Eval2.eval(code, 0));
+    }
+
+    @Test public void testInt10() {
+        CodeGen code = new CodeGen("flt x = 1.5; x++; int i = x; return i;");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Type 2.5f is not of declared type int",e.getMessage()); }
+    }
+
+
+    // ---------------------------------------------------------------
+    @Test public void testVar0() {
+        CodeGen code = new CodeGen("var d; return d;");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected =expression: ;",e.getMessage()); }
+    }
+
+    @Test public void testVar1() {
+        CodeGen code = new CodeGen("val d; return d;");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected =expression: ;",e.getMessage()); }
+    }
+
+    @Test public void testVar2() {
+        CodeGen code = new CodeGen("int x; x=3; x++; return x; // Ok, no initializer so x is mutable ");
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+        assertEquals("4", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar3() {
+        CodeGen code = new CodeGen("int x=3; x++; return x; // Ok, primitive so x is mutable despite initializer ");
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+        assertEquals("4", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar4() {
+        CodeGen code = new CodeGen("struct S{int x;}; S? s; s=new S; s.x++; return s.x; // Ok, no initializer so x is mutable ");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar5() {
+        CodeGen code = new CodeGen("struct S{int x;}; S? s; s=new S{x=3;}; s.x++; return s.x; // Ok, no initializer so x is mutable ");
+        code.parse().opto();
+        assertEquals("return 4;", code.print());
+        assertEquals("4", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar6() {
+        CodeGen code = new CodeGen("struct S{int x;}; S s=new S; s.x++; return s.x; // Error initializer so x is immutable ");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar7() {
+        CodeGen code = new CodeGen("struct S{int x;}; S s=new S{x=3;}; s.x++; return s.x; // Error initializer so x is immutable ");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar8() {
+        CodeGen code = new CodeGen("struct S{int x;}; S !s=new S; s.x++; return s.x; // Ok, has '!' so s.x is mutable ");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar9() {
+        CodeGen code = new CodeGen("struct S{int x;}; var s=new S; s.x++; return s.x; // Ok, has var so s.x is mutable ");
+        code.parse().opto();
+        assertEquals("return 1;", code.print());
+        assertEquals("1", Eval2.eval(code, 0));
+    }
+
+    @Test public void testVar10() {
+        CodeGen code = new CodeGen("struct S{int x;}; val s=new S; s.x++; return s.x; // Error, has val so x is immutable ");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar11() {
+        CodeGen code = new CodeGen("""
+struct Bar { int x; };
+Bar !bar = new Bar;
+bar.x = 3; // Ok, bar is mutable
+
+struct Foo { Bar? !bar; int y; };
+Foo !foo = new Foo { bar = bar; };
+foo.bar = bar; // Ok foo is mutable
+foo.bar.x++;   // Ok foo and foo.bar and foo.bar.x are all mutable
+
+val xfoo = foo; // Throw away mutability
+xfoo.bar.x++;   // Error, cannot mutate through xfoo
+ """);
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot modify final field 'x'",e.getMessage()); }
+    }
+
+    @Test public void testVar12() {
+        CodeGen code = new CodeGen("""
+struct Bar { int x; };
+Bar !bar = new Bar;
+bar.x = 3; // Ok, bar is mutable
+
+struct Foo { Bar? !bar; int y; };
+Foo !foo = new Foo;
+foo.bar = bar; // Ok bar is mutable
+foo.bar.x++;   // Ok foo and foo.bar and foo.bar.x are all mutable
+
+val xfoo = foo;        // Throw away mutability
+int x4 = xfoo.bar.x;   // Ok to read through xfoo, gets 4
+foo.bar.x++;           // Bumps to 5
+int x5 = xfoo.bar.x;   // Ok to read through xfoo, gets 5
+return x4*10+x5;
+""");
+        code.parse().opto();
+        assertEquals("return 45;", code.print());
+        assertEquals("45", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testVar13() {
+        CodeGen code = new CodeGen("""
+int i,i++;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Redefining name 'i'",e.getMessage()); }
+    }
+
+
+    @Test
+    public void testVar14() {
+        CodeGen code = new CodeGen("""
+struct B {};
+struct A { B b; };
+A x = new A {
+    return b; // read before init
+    b = new B;
+};
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot read uninitialized field 'b'",e.getMessage()); }
+    }
+
+    @Test
+    public void testVar15() {
+        CodeGen code = new CodeGen("""
+struct B {};
+struct A { B b; };
+return new A {
+    if (arg) b = new B; // Constructor ends with partial init of b
+}.b;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("'A' is not fully initialized, field 'b' needs to be set in a constructor",e.getMessage()); }
+    }
+
+    @Test
+    public void testVar16() {
+        CodeGen code = new CodeGen(
+"""
+struct S{};
+val x = 1;
+val s = new S{x = 2;};
+return x;
+"""
+);
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Cannot reassign final 'x'",e.getMessage()); }
+    }
+
+    @Test
+    public void testVar17() {
+        CodeGen code = new CodeGen(
+"""
+struct Person {
+    bool focused;
+};
+val focus = { Person p ->
+    p.focused = true;
+};
+Person me; // Person !me = new Person;
+focus(me);
+return me;
+"""
+);
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected =expression: ;",e.getMessage()); }
+    }
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testTrinary0() {
+        CodeGen code = new CodeGen("""
+return arg ? 1 : 2;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,1,2);", code.print());
+        assertEquals("2", Eval2.eval(code, 0));
+        assertEquals("1", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testTrinary1() {
+        CodeGen code = new CodeGen("""
+return arg ? 0 : arg;
+""");
+        code.parse().opto();
+        assertEquals("return 0;", code.print());
+        assertEquals("0", Eval2.eval(code, 0));
+    }
+
+    @Test
+    public void testTrinary2() {
+        CodeGen code = new CodeGen("""
+struct Bar { int x; };
+var b = arg ? new Bar : null;
+return b ? b.x++ + b.x++ : -1;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,((.x<<1)+1),-1);", code.print());
+        assertEquals("-1", Eval2.eval(code, 0));
+        assertEquals("1", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testTrinary3() {
+        CodeGen code = new CodeGen("""
+struct Bar { int x; };
+var b = arg ? new Bar;
+return b ? b.x++ + b.x++ : -1;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,((.x<<1)+1),-1);", code.print());
+        assertEquals("-1", Eval2.eval(code, 0));
+        assertEquals("1", Eval2.eval(code, 1));
+    }
+
+    @Test
+    public void testTrinary4() {
+        // This test case will benefit from an unzipping transformation
+        CodeGen code = new CodeGen("""
+struct Bar { Bar? next; int x; };
+var b = arg ? new Bar { next = (arg==2) ? new Bar{x=2;}; x=1; };
+return b ? b.next ? b.next.x : b.x; // parses "b ? (b.next ? b.next.x : b.x) : 0"
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,Phi(Region,.x,.x),0);", code.print());
+        assertEquals("0", Eval2.eval(code, 0));
+        assertEquals("1", Eval2.eval(code, 1));
+        assertEquals("2", Eval2.eval(code, 2));
+    }
+
+    @Test
+    public void testTrinary5() {
+        CodeGen code = new CodeGen("""
+flt f=arg?1:1.2;
+return f;   // missing widening
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Region,1.0f,1.2);", code.print());
+        assertEquals("1.2", Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testTrinary6() {
+        CodeGen code = new CodeGen("""
+struct S{};
+return arg ? 7 : new S;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("No common type amongst int and reference",e.getMessage()); }
+    }
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testFor0() {
+        CodeGen code = new CodeGen("""
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", code.print());
+        assertEquals("3", Eval2.eval(code, 3));
+        assertEquals("45", Eval2.eval(code, 10));
+    }
+    @Test
+    public void testFor1() {
+        CodeGen code = new CodeGen("""
+int sum=0, i=0;
+for( ; i<arg; i++ )
+    sum += i;
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", code.print());
+        assertEquals("3", Eval2.eval(code, 3));
+        assertEquals("45", Eval2.eval(code, 10));
+    }
+    @Test
+    public void testFor2() {
+        CodeGen code = new CodeGen("""
+int sum=0;
+for( int i=0; ; i++ ) {
+    if( i>=arg ) break;
+    sum += i;
+}
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", code.print());
+        assertEquals("3", Eval2.eval(code, 3));
+        assertEquals("45", Eval2.eval(code, 10));
+    }
+    @Test
+    public void testFor3() {
+        CodeGen code = new CodeGen("""
+int sum=0;
+for( int i=0; i<arg; )
+    sum += i++;
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_sum+Phi(Loop,0,(Phi_i+1))));", code.print());
+        assertEquals("3", Eval2.eval(code, 3));
+        assertEquals("45", Eval2.eval(code, 10));
+    }
+    @Test
+    public void testFor4() {
+        CodeGen code = new CodeGen("""
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return i;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Undefined name 'i'",e.getMessage()); }
+    }
+    @Test
+    public void testFor5() {
+        CodeGen code = new CodeGen("""
+for(;;arg++;) {}
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Syntax error, expected Unexpected code after expression: ;",e.getMessage()); }
+    }
+
+
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testForward0() {
+        CodeGen code = new CodeGen("""
+struct A{
+    B? f1;
+    B? f2;
+};
+return new A;
+""");
+        code.parse().opto();
+        assertEquals("return A;", code.print());
+        assertEquals("A{f1=null,f2=null}", Eval2.eval(code,0));
+    }
+
+    @Test
+    public void testForward1() {
+        CodeGen code = new CodeGen("""
+struct A{
+    B?[]? nil_array_of_b;
+    B?[]  not_array_of_b = new B?[0];
+};
+return new A.not_array_of_b;
+""");
+        code.parse().opto();
+        assertEquals("return (const)[*B?];", code.print());
+        assertEquals("*B?[]", Eval2.eval(code,0));
+    }
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testLinkedList2() {
+        CodeGen code = new CodeGen("""
+struct LLI { LLI? next; int i; };
+LLI? !head = null;
+while( arg-- )
+    head = new LLI { next=head; i=arg; };
+int sum=0;
+var ptr = head; // A read-only ptr, to be assigned from read-only next fields
+for( ; ptr; ptr = ptr.next )
+    sum += ptr.i;
+return sum;
+""");
+        code.parse().opto();
+        assertEquals("return Phi(Loop,0,(Phi_sum+.i));", code.print());
+        assertEquals("45", Eval2.eval(code, 10));
+    }
+
+    @Test
+    public void sieveOfEratosthenes() {
+        CodeGen code = new CodeGen(
+"""
+var ary = new bool[arg], primes = new int[arg];
+var nprimes=0, p=0;
+// Find primes while p^2 < arg
+for( p=2; p*p < arg; p++ ) {
+    // skip marked non-primes
+    while( ary[p] ) p++;
+    // p is now a prime
+    primes[nprimes++] = p;
+    // Mark out the rest non-primes
+    for( int i = p + p; i < ary#; i += p )
+        ary[i] = true;
+}
+// Now just collect the remaining primes, no more marking
+for( ; p < arg; p++ )
+    if( !ary[p] )
+        primes[nprimes++] = p;
+// Copy/shrink the result array
+var !rez = new int[nprimes];
+for( int j=0; j<nprimes; j++ )
+    rez[j] = primes[j];
+return rez;
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return [int];", code.print());
+        assertEquals("int[ 2,3,5,7,11,13,17,19]",Eval2.eval(code, 20));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter18Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter18Test.java
new file mode 100644
index 00000000..db970f60
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter18Test.java
@@ -0,0 +1,369 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+import static org.junit.Assert.fail;
+import org.junit.Ignore;
+
+public class Chapter18Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen(
+"""
+return 0;
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return 0;", code._stop.toString());
+        assertEquals("0", Eval2.eval(code,  2));
+    }
+
+    @Test
+    public void testPhiParalleAssign() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+int b = 2;
+while(arg--) {
+  int t = a;
+  a = b;
+  b = t;
+}
+return a;
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return Phi(Loop,1,Phi(Loop,2,Phi_a));", code._stop.toString());
+        assertEquals("1", Eval2.eval(code,  0));
+        assertEquals("2", Eval2.eval(code,  1));
+        assertEquals("1", Eval2.eval(code,  2));
+        assertEquals("2", Eval2.eval(code,  3));
+    }
+
+
+    // ---------------------------------------------------------------
+    @Test
+    public void testType0() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? x2 = null; // null function ptr
+return x2;
+""");
+        code.parse().opto();
+        assertEquals("return null;", code._stop.toString());
+        assertEquals("null", Eval2.eval(code, 0 ) );
+    }
+
+    @Test
+    public void testFcn0() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? sq = { int x ->
+    x*x;
+};
+return sq;
+""");
+        code.parse().opto();
+        assertEquals("Stop[ return { sq}; return (Parm_x(sq,int)*x); ]", code._stop.toString());
+        assertEquals("{ int -> int #1}", Eval2.eval(code, 3));
+    }
+
+    @Test
+    public void testFcn1() {
+        CodeGen code = new CodeGen(
+"""
+var sq = { int x ->
+    x*x;
+};
+return sq(arg)+sq(3);
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("Stop[ return (sq( 3)+sq( arg)); return (Parm_x(sq,int,3,arg)*x); ]", code._stop.toString());
+        assertEquals("13", Eval2.eval(code, 2));
+    }
+
+    // Function scope test
+    @Test
+    public void testFcn2() {
+        CodeGen code = new CodeGen(
+"""
+int cnt=1;
+return { -> cnt; };
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("Variable 'cnt' is out of function scope and must be a final constant",e.getMessage()); }
+    }
+
+    // Function scope test
+    @Test
+    public void testFcn3() {
+        CodeGen code = new CodeGen(
+"""
+val cnt=2;
+return { -> cnt; }();
+""");
+        code.parse().opto();
+        assertEquals("return 2;", code._stop.toString());
+        assertEquals("2", Eval2.eval(code, 0));
+    }
+
+    // Function variables
+    @Test
+    public void testFcn4() {
+        CodeGen code = new CodeGen(
+"""
+var fcn = arg ? { int x -> x*x; } : { int x -> x+x; };
+return fcn(3);
+""");
+        code.parse().opto();
+        assertEquals("Stop[ return Phi(Region,{ int -> int #1},{ int -> int #2})( 3); return (Parm_x($fun,int,3)*x); return (Parm_x($fun,int,3)<<1); ]", code._stop.toString());
+        assertEquals("6", Eval2.eval(code, 0));
+        assertEquals("9", Eval2.eval(code, 1));
+    }
+
+    // Recursive factorial test
+    @Test
+    public void testFcn5() {
+        CodeGen code = new CodeGen("val fact = { int x -> x <= 1 ? 1 : x*fact(x-1); }; return fact(arg);");
+        code.parse().opto().typeCheck();
+        assertEquals("Stop[ return fact( arg); return Phi(Region,1,(Parm_x(fact,int,arg,(x-1))*fact( Sub))); ]", code._stop.toString());
+        assertEquals( "1", Eval2.eval(code, 0));
+        assertEquals( "1", Eval2.eval(code, 1));
+        assertEquals( "2", Eval2.eval(code, 2));
+        assertEquals( "6", Eval2.eval(code, 3));
+        assertEquals("24", Eval2.eval(code, 4));
+    }
+
+    @Test
+    public void testFcn6() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int i; };
+val newS = { int x -> return new S { i=x; }; };
+return newS(1).i;
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return 1;", code._stop.toString());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    // Double forward reference
+    @Test
+    public void testFcn7() {
+        CodeGen code = new CodeGen(
+"""
+if( arg ? f : g ) return 1;
+val f = {->1;};
+val g = {->2;};
+return 2;
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("Stop[ return 1; return 1; return 2; ]", code._stop.toString());
+        assertEquals("1", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testFcn8() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? i2i = null;
+var id = {{int->int} f-> return f;};
+for(;;) {
+    if (i2i) return i2i(arg);
+    var x = {int i-> return i;};
+    arg = x(3);
+    i2i = id(x);
+}
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("Stop[ return x( Phi(Loop,arg,x( 3))); return Parm_i(x,int,3,Phi_arg); ]", code._stop.toString());
+        assertEquals("3", Eval2.eval(code,  0));
+    }
+
+    @Test
+    public void testFcn9() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? i2i = null;
+for(;;) {
+    if (i2i) return i2i(arg);
+    var x = {int i-> return i;};
+    arg = x(3);
+}
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return Top;", code._stop.toString());
+        assertEquals(null, Eval2.eval(code,  0));
+    }
+
+
+    @Test
+    public void testFcn10() {
+        CodeGen code = new CodeGen(
+"""
+struct Person {
+  int age;
+};
+
+val fcn = { Person?[] ps, int x ->
+  val tmp = ps[x];
+  if( ps[x] )
+    ps[x].age++;
+};
+
+var ps = new Person?[2];
+ps[0] = new Person;
+ps[1] = new Person;
+fcn(ps,1);
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return 0;", code._stop.toString());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    // Function break
+    @Test
+    public void testErr1() {
+        CodeGen code = new CodeGen(
+"""
+for(;;) {
+    val f = { ->
+        break;
+    };
+    f();
+    return 2;
+}
+return 1;
+""");
+        try { code.parse().opto(); fail(); }
+        catch( Exception e ) { assertEquals("No active loop for a break or continue",e.getMessage()); }
+    }
+
+    // Calling and inlining a null function
+    @Test
+    public void testErr2() {
+        CodeGen code = new CodeGen(
+"""
+{int -> int}? !i2i = { int i -> return i; };
+for(;;) {
+    if (i2i(2) == arg) break;
+    i2i = null;
+}
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Might be null calling { int -> int #1}?",e.getMessage()); }
+    }
+
+
+    @Test
+    public void testErr3() {
+        CodeGen code = new CodeGen(
+"""
+val f = { int i, int j -> return i+j; };
+return f();
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Expecting 2 arguments, but found 0",e.getMessage()); }
+    }
+
+
+    @Test
+    public void testErr4() {
+        CodeGen code = new CodeGen(
+"""
+struct S {
+    {int} f = { -> x(); return 0; }; // Do not let fref x be a field
+};
+val x = { -> return 1; };
+S? s = null;
+for(;;) {
+    if (s) return s.x;
+}
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("Accessing unknown field 'x' from '*S'",e.getMessage()); }
+    }
+
+    @Test
+    public void testErr5() {
+        CodeGen code = new CodeGen(
+"""
+val g = { ->
+    g();
+};
+return 0;
+""");
+        try { code.parse().opto().typeCheck(); fail(); }
+        catch( Exception e ) { assertEquals("No defined return type",e.getMessage()); }
+    }
+
+
+    // Mutual recursion.  Fails without SCCP to lift the recursive return types.
+    @Ignore @Test
+    public void testFcnMutRec() {
+        CodeGen code = new CodeGen(
+"""
+val is_even = { int x -> x ? is_odd (x-1) : true ; };
+val is_odd  = { int x -> x ? is_even(x-1) : false; };
+return is_even(arg);
+""");
+        code.parse().opto();
+        assertEquals("Stop[ return is_even( arg); return Phi(Region,Phi(Region,is_even( ((Parm_x(is_even,int,arg,Sub)-1)-1)),0),1); ]", code._stop.toString());
+        assertEquals("1", Eval2.eval(code, 0));
+        assertEquals("0", Eval2.eval(code, 1));
+        assertEquals("1", Eval2.eval(code, 2));
+        assertEquals("0", Eval2.eval(code, 3));
+    }
+
+    // Forward ref to 'x' means that
+    @Ignore @Test
+    public void testForwardRef1() {
+        CodeGen code = new CodeGen(
+"""
+struct S {
+    { int } f = { -> return x(); };
+};
+val x = { -> return 1; };
+S? s = null;
+for(;;) {
+    if (s) return s.f;
+}
+""");
+        code.parse().opto().typeCheck().GCM();
+        assertEquals("return 0;", code._stop.toString());
+        assertEquals("0", Eval2.eval(code,  0));
+    }
+
+    // Inline hidden called more than once
+    @Test
+    public void testInline() {
+        CodeGen code = new CodeGen(
+"""
+{int->int}?! i2i = {int i->return i;};
+{{int->int}->{int->int}}! f2f = {{int->int} f->return f;};
+val o = i2i;
+if (arg) i2i = null;
+if (i2i) return i2i(arg);
+return f2f(o)(1);
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("Stop[ return Phi(Region,o( arg),o( 1)); return Parm_i(o,int,arg,1); ]", code._stop.toString());
+        assertEquals("1", Eval2.eval(code,  2));
+    }
+
+    @Test
+    public void testOperField() {
+        CodeGen code = new CodeGen(
+"""
+struct Person {
+    int coffee_count;
+};
+Person !p = new Person;
+p.coffee_count += 1;
+return p.coffee_count;
+""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("return 1;", code._stop.toString());
+        assertEquals("1", Eval2.eval(code,  2));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter19Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter19Test.java
new file mode 100644
index 00000000..a4857a01
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter19Test.java
@@ -0,0 +1,398 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+import static org.junit.Assert.fail;
+import org.junit.Ignore;
+
+public class Chapter19Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen("""
+return 0;
+""");
+        code.parse().opto().typeCheck();
+        assertEquals("return 0;", code._stop.toString());
+        assertEquals("0", Eval2.eval(code,  2));
+    }
+
+
+    @Test
+    public void testString() {
+        CodeGen code = new CodeGen(
+"""
+struct String {
+    u8[] cs;
+    int _hashCode;
+};
+
+val equals = { String self, String s ->
+    if( self == s ) return true;
+    if( self.cs# != s.cs# ) return false;
+    for( int i=0; i< self.cs#; i++ )
+        if( self.cs[i] != s.cs[i] )
+            return false;
+    return true;
+};
+
+val hashCode = { String self ->
+    self._hashCode
+    ?  self._hashCode
+    : (self._hashCode = _hashCodeString(self));
+};
+
+val _hashCodeString = { String self ->
+    int hash=0;
+    if( self.cs ) {
+        for( int i=0; i< self.cs#; i++ )
+            hash = hash*31 + self.cs[i];
+    }
+    if( !hash ) hash = 123456789;
+    return hash;
+};
+
+String !s = new String { cs = new u8[17]; };
+s.cs[0] =  67; // C
+s.cs[1] = 108; // l
+hashCode(s);""");
+        code.parse().opto().typeCheck().GCM().localSched();
+        assertEquals("Stop[ return Phi(Region,123456789,Phi(Loop,0,(.[]+((Phi_hash<<5)-Phi_hash)))); return Phi(Region,1,0,0,1); ]", code._stop.toString());
+        assertEquals("-2449306563677080489", Eval2.eval(code,  2));
+    }
+
+    @Test
+    public void testBasic0() {
+        CodeGen code = new CodeGen("return 0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return 0;", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic1() {
+        CodeGen code = new CodeGen("return arg+1;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (inc,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic2() {
+        CodeGen code = new CodeGen("return -17;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return -17;", code._stop.toString());
+    }
+
+
+    @Test
+    public void testBasic3() {
+        CodeGen code = new CodeGen("return arg==1;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (set==,(cmp,arg));", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic4() {
+        CodeGen code = new CodeGen("return arg<<1;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (shli,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic5() {
+        CodeGen code = new CodeGen("return arg >> 1;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (sari,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic6() {
+        CodeGen code = new CodeGen("return arg >>> 1;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (shri,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic7() {
+        CodeGen code = new CodeGen("return arg / 2;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (div,arg,2);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic8() {
+        CodeGen code = new CodeGen("return arg * 6;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (muli,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic9() {
+        CodeGen code = new CodeGen("return arg & 2;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (andi,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic10() {
+        CodeGen code = new CodeGen("return arg | 2;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (ori,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic11() {
+        CodeGen code = new CodeGen("return arg ^ 2;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (xori,arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic12() {
+        CodeGen code = new CodeGen("return arg + 2.0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (addf,(i2f8,arg),2.0f);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic13() {
+        CodeGen code = new CodeGen("return arg - 2.0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (subf,(i2f8,arg),2.0f);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic14() {
+        CodeGen code = new CodeGen("return arg * 2.0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (mulf,(i2f8,arg),2.0f);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic15() {
+        CodeGen code = new CodeGen("return arg / 2.0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (divf,(i2f8,arg),2.0f);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic16() {
+        CodeGen code = new CodeGen(
+"""
+int arg1 =  arg + 1;
+return arg1 / arg;""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (div,(inc,arg),arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testBasic17() {
+        CodeGen code = new CodeGen(
+"""
+int arg1 =  arg + 1;
+return arg1 * arg;
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (mul,(inc,arg),arg);", code._stop.toString());
+    }
+
+    @Test
+    public void testToFloat() {
+        CodeGen code = new CodeGen("""
+                int a = arg;
+                return a + 2.0;
+                """
+        ).parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (addf,(i2f8,arg),2.0f);", code._stop.toString());
+    }
+
+    @Test
+    public void testIfStmt() {
+        CodeGen code = new CodeGen(
+"""
+int a = 1;
+if (arg == 1)
+    a = arg+2;
+else {
+    a = arg-3;
+}
+return a;""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return Phi(Region,(addi,arg),(addi,arg));", code.print());
+    }
+
+    @Test
+    public void testIfMerge2() {
+        CodeGen code = new CodeGen(
+"""
+int a=arg+1;
+int b=arg+2;
+if( arg==1 )
+    b=b+a;
+else
+    a=b+1;
+return a+b;""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (add,(add,Phi(Region,(shli,arg),arg),arg),Phi(Region,4,5));", code.print());
+    }
+
+    @Test
+    public void testLoop() {
+        CodeGen code = new CodeGen(
+"""
+int sum=0;
+for( int i=0; i<arg; i++ )
+    sum += i;
+return sum;""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return Phi(Loop,0,(add,Phi_sum,Phi(Loop,0,(inc,Phi_i))));", code.print());
+    }
+
+    @Test
+    public void testAlloc1() {
+        CodeGen code = new CodeGen(
+"""
+struct S { int a; S? c; };
+return new S;""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return S;", code.print());
+    }
+
+    @Test
+    public void testLea1() {
+        CodeGen code = new CodeGen("int x = arg/3; return arg+x+7;");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2",  "SystemV").GCM().localSched();
+        assertEquals("return (lea,arg,(div,arg,3));", code.print());
+    }
+
+    @Test
+    public void testLea2() {
+        CodeGen code = new CodeGen("int x = arg/3; return arg+x*4+7;");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return (lea,arg,(div,arg,3));", code.print());
+    }
+
+    @Test
+    public void testLea3() {
+        CodeGen code = new CodeGen("int x = arg/3; return x*4+arg;");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2",  "SystemV").GCM().localSched();
+        assertEquals("return (lea,arg,(div,arg,3));", code.print());
+    }
+
+    @Test
+    public void testAlloc2() {
+        CodeGen code = new CodeGen("int[] !xs = new int[3]; xs[arg]=1; return xs[arg&1];");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return .[];", code.print());
+    }
+
+    @Test
+    public void testAlloc3() {
+        CodeGen code = new CodeGen("int[] !xs = new int[3]; xs[arg]=1; return xs[arg&1]+3;");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return .[];", code.print());
+    }
+
+    @Test
+    public void testArray1() {
+        CodeGen code = new CodeGen(
+"""
+int[] !ary = new int[arg];
+// Fill [0,1,2,3,4,...]
+for( int i=0; i<ary#; i++ )
+    ary[i] = i;
+// Fill [0,1,3,6,10,...]
+for( int i=0; i<ary#-1; i++ )
+    ary[i+1] += ary[i];
+return ary[1] * 1000 + ary[3]; // 1 * 1000 + 6
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return .[];", code.print());
+    }
+
+    @Test
+    public void testArray2() {
+        CodeGen code = new CodeGen(
+"""
+flt[] !A = new flt[arg], !B = new flt[arg];
+// Fill [0,1,2,3,4,...]
+for( int i=0; i<A#; i++ )
+    A[i] = i;
+for( int i=0; i<A#; i++ )
+    B[i] += A[i];
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return 0;", code.print());
+    }
+
+    @Test
+    public void testArray3() {
+        CodeGen code = new CodeGen(
+"""
+byte[] !A = new byte[arg];
+for( int i=0; i<A#; i++ )
+    A[i]++;
+return A[1];
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return .[];", code.print());
+    }
+
+    @Test
+    public void testNewton() {
+        CodeGen code = new CodeGen(
+"""
+// Newtons approximation to the square root
+val sqrt = { flt x ->
+    flt guess = x;
+    while( 1 ) {
+        flt next = (x/guess + guess)/2;
+        if( next == guess ) return guess;
+        guess = next;
+    }
+};
+flt farg = arg;
+return sqrt(farg);
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return Phi(Loop,(i2f8,arg),(divf,(addf,(divf,i2f8,Phi_guess),Phi_guess),2.0f));", code.print());
+    };
+
+
+    @Test
+    public void sieveOfEratosthenes() {
+        CodeGen code = new CodeGen(
+"""
+var ary = new bool[arg], primes = new int[arg];
+var nprimes=0, p=0;
+// Find primes while p^2 < arg
+for( p=2; p*p < arg; p++ ) {
+    // skip marked non-primes
+    while( ary[p] ) p++;
+    // p is now a prime
+    primes[nprimes++] = p;
+    // Mark out the rest non-primes
+    for( int i = p + p; i < ary#; i += p )
+        ary[i] = true;
+}
+// Now just collect the remaining primes, no more marking
+for( ; p < arg; p++ )
+    if( !ary[p] )
+        primes[nprimes++] = p;
+// Copy/shrink the result array
+var !rez = new int[nprimes];
+for( int j=0; j<nprimes; j++ )
+    rez[j] = primes[j];
+return rez;
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("return [int];", code.print());
+        //assertEquals("int[ 2,3,5,7,11,13,17,19]",Eval2.eval(code, 20));
+    }
+
+
+    @Test
+    public void testFcn1() {
+        CodeGen code = new CodeGen(
+"""
+val fcn = arg ? { int x -> x*x; } : { int x -> x+x; };
+return fcn(2)*10 + fcn(3);
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("Stop[ return (add,Phi(Region,{ int -> int #1},{ int -> int #2})( 3),(muli,Phi_( 2))); return (mul,Parm_x($fun,int,3,2),x); return (shli,Parm_x($fun,int,3,2)); ]", code.print());
+    }
+
+    @Test
+    public void testFcn2() {
+        CodeGen code = new CodeGen(
+"""
+val sq = { int x -> x*x; };
+return sq(arg) + sq(3);
+""");
+        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        assertEquals("Stop[ return (add,sq(),sq()); return (mul,Parm_x(sq,int,3,arg),x); ]", code.print());
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Chapter20Test.java b/chapter20/src/test/java/com/seaofnodes/simple/Chapter20Test.java
new file mode 100644
index 00000000..48458f95
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Chapter20Test.java
@@ -0,0 +1,17 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.*;
+
+public class Chapter20Test {
+
+    @Test
+    public void testJig() {
+        CodeGen code = new CodeGen("""
+return 0;
+""");
+        code.parse().opto().typeCheck();
+        assertEquals("return 0;", code._stop.toString());
+        assertEquals("0", Eval2.eval(code,  2));
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Eval2.java b/chapter20/src/test/java/com/seaofnodes/simple/Eval2.java
new file mode 100644
index 00000000..6ae8427c
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Eval2.java
@@ -0,0 +1,448 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.type.*;
+import com.seaofnodes.simple.node.*;
+import java.util.*;
+
+public abstract class Eval2 {
+
+    // A mapping from Node ID to evaluation data Object.
+    // Data Objsts are a boxed Long or Double; or an Object[] of fields, which
+    // themselves are just more Objects.
+    private static class Frame {
+        private static int UID=1;
+
+        private final IdentityHashMap<Node,Object> _data;
+        private Frame _prior;   // Prior frame in this sequence, means when making a new frame we can find old stuff
+        private int _refcnt;    // TODO: Use this in a sentence (free/recycle unused stack frames)
+        final int _uid = UID++; // Debugging aid
+        Frame(Frame prior) {
+            _prior = prior;
+            if( prior!=null ) prior._refcnt++;
+            _data = new IdentityHashMap<>();
+            _refcnt = 1;
+        }
+
+        // Dec ref count
+        void dec() {
+            assert _refcnt>0;
+            if( --_refcnt == 0 ) {
+                Frame prior = _prior;
+                _prior = null;
+                _data.clear();
+                // TODO: FREE LIST?
+                if( prior!=null )
+                    prior.dec();
+            }
+        }
+
+        // Put a mapping from Node->Object
+        Node put(Node n, Object d) {
+            assert d!=null;
+            return put0(n,d);
+        }
+        // Put a mapping from Node->Object?
+        Node put0(Node n, Object d) {
+            assert _refcnt>0;
+            _data.put(n,d);
+            return n;
+        }
+        // Get a mapped Node, perhaps using the prior stack frame crawl
+        Object get(Node n) {
+            assert _refcnt>0;
+            Object d = _data.get(n);
+            return d != null ? d
+                : _prior == null ? null
+                : _prior.get(n);
+        }
+
+        // Short debugging print
+        public String p() {
+            return "#"+_uid + (_prior==null ? "" : " >> " + _prior.p());
+        }
+        // Long debugging print
+        @Override public String toString() {
+            String s = "";
+            if( _prior != null ) s+= _prior+" << ";
+            s += "#"+_uid+"[ ";
+            for( Node n : _data.keySet() )
+                s += n + ":" + _data.get(n) + ",";
+            s += "]";
+
+            return s;
+        }
+    }
+
+    // Classic Closure; an environment (stack of frames) and an execution point
+    private static class Closure {
+        // Where to return too; either a CallEnd or a Function
+        final CFGNode _cc;
+
+        // Stack frame at the execution point.  Includes Closures which
+        // recursively include other stack frames
+        private Frame _frame;
+
+        Closure(CFGNode cc, Frame frame) {
+            _cc = cc;           // One of Fun, CallEnd or Stop (null)
+            _frame = frame;
+            assert _frame._refcnt >=0;
+            _frame._refcnt++;
+        }
+
+        FunNode fun() { return (FunNode)_cc; }
+        CallEndNode cend() { return (CallEndNode)_cc; }
+        boolean isStop() { return _cc instanceof StopNode; } // or Stop
+
+        //
+        void pushFrame() {
+            _frame = new Frame(_frame);
+            _frame._refcnt++;
+        }
+
+        @Override public String toString() {
+            return _cc.toString();
+        }
+    }
+
+    // CodeGen has the linker tables
+    public static CodeGen CODE;
+
+    // Current active Frame, to avoid having to pass it everywhere
+    public static Frame F;
+
+    public static String eval( CodeGen code, long arg ) { return eval(code,arg,1000); }
+    public static String eval( CodeGen code, long arg, int timeout ) {
+        SB trace = null; // new SB(); // TRACE, set to null for off, new SB() for on
+        // Force local scheduling phase
+        if( code._phase.ordinal() < CodeGen.Phase.TypeCheck .ordinal() )  code.typeCheck();
+        if( code._phase.ordinal() < CodeGen.Phase.Schedule  .ordinal() )  code.GCM();
+        if( code._phase.ordinal() < CodeGen.Phase.LocalSched.ordinal() )  code.localSched();
+        // Set global, so don't have to pass everywhere
+        CODE = code;
+
+        // Timer for when we run too long.  Ticks once per backedge or function call
+        int loopCnt = 0;
+
+        // Current value for each Node; boxed Long or Double; or an Object[] of
+        // fields, which themselves are just more Objects.
+        F = new Frame(null);
+
+        // Start at the START
+        CFGNode BB = code._start, prior = null;
+        // Return from main hits Stop
+        F.put(BB,new Closure(code._stop,F));
+
+
+        // ------------
+        // Evaluate until exit or timeout.  Each outer loop step computes
+        // all data nodes under some new Control.
+        while( true ) {
+            assert BB!=null;
+            traceCtrl(BB,trace);
+            if( trace!=null ) System.out.println(F.p());
+
+            // Parallel assign Phis
+            int i = BB instanceof RegionNode r
+                    ? parallelAssignPhis(r,prior,arg,trace)
+                    : 0;
+
+            // Compute the data nodes until BB control
+            for( ; i < BB.nOuts(); i++ )
+                if( !(BB.out(i) instanceof CFGNode) )
+                    step(BB.out(i), trace);
+
+            // Find the next control target
+            prior = BB;
+            BB = BB.uctrl();      // Next unique control target
+            switch( prior ) {
+            case StartNode start:  F = new Frame(F); break; // Frame for the call to main, as-if Called
+            case CallNode  call :  BB = call(call); break;
+            case IfNode    iff  :  Object p = val(iff.pred()); BB = iff.cproj( p==null || (p instanceof Long x && x==0L)  ? 1 : 0);  break;
+            case ReturnNode ret :  if( clj(ret.rpc()).isStop() ) return exit(ret); else BB = ret(ret); break;
+            case FunNode   fun  :  if( loopCnt++ > timeout ) return null;  break; // Timeout
+            case LoopNode  loop :  if( loopCnt++ > timeout ) return null;  break; // Timeout
+            case CallEndNode cend: break;
+            case CProjNode cproj:  break;
+            case RegionNode r   :  break;
+            default:               throw Utils.TODO();
+            }
+            assert !BB.isDead();
+        }
+    }
+
+
+    // Phi cache; size is limited to number of Phis at a merge point
+    private static final Object[] PHICACHE = new Object[256];
+    static int parallelAssignPhis(RegionNode r, CFGNode prior, long arg, SB trace) {
+
+        // Compute input path on Phis for this Region
+        int path = r._inputs.find( prior );
+        // Parameters read from prior frame, Phis from local frame
+        Frame frame = (r instanceof FunNode ? F._prior : F);
+        boolean isMain = r instanceof FunNode fun && fun.sig().isa(CodeGen.CODE._main);
+
+        // Parallel assign Phis.  First parallel read and cache
+        int i;
+        for( i = 0; i < r.nOuts(); i++ ) {
+            if( !(r.out(i) instanceof PhiNode phi) ) break;
+            if( isMain && phi instanceof ParmNode parm && parm._idx==2 )
+                PHICACHE[i] = arg; // Reading the initial arguments to main()
+            else {
+                Node n = phi instanceof ParmNode parm
+                    // RPC reads the Call directly;
+                    // Parms may not be linked, so read call args directly
+                    ? (parm._idx==0 ? prior : prior.in(parm._idx))
+                    // Phis read from path input
+                    :  phi.in(path);
+                PHICACHE[i] = frame.get(n);
+            }
+        }
+        // Parallel assign; might assign before read, so read from cache
+        for( int j=0; j < i; j++ )
+            traceData(F.put0(r.out(j),PHICACHE[j]),trace);
+        // Return point in basic block past last Phi
+        return i;
+    }
+
+
+    // Make a call.
+    private static CFGNode call( CallNode call ) {
+        // Set up the Return PC and return frame (which is just the current frame).
+        // Really making a Continuation, but it's just a Closure
+        Closure cont = new Closure(call.cend(),F);
+        // Set the return continuation into the current frame RPC
+        F.put(call, cont );
+        // Next Frame to use
+        F = new Frame(F);
+        // Target function and environment
+        return CODE.link(tfp(call.fptr()));
+    }
+
+    private static CFGNode ret( ReturnNode ret ) {
+        // Fetch return expression value and continuation from current frame
+        Object rez = val(ret.expr());
+        Closure cont = clj(ret.rpc());
+        // Lower Frame reference count; might delete frame
+        F.dec();                // Lower ref count
+        // Install replacement Frame; set return result over the CallEnd
+        F = cont._frame;
+        F.put0(cont._cc,rez);   // Set return value into CallEnd
+        return cont._cc;        // Return CallEnd as the new control
+    }
+
+    private static String exit( ReturnNode ret ) {
+        return prettyPrint(ret.expr()._type,val(ret.expr()));
+    }
+
+    // Take a worklist step: one data op from the current Control is updated.
+    private static void step(Node n, SB trace) {
+        if( n instanceof PhiNode ) return;
+        // Compute new value
+        F.put0(n,compute(n));
+        traceData(n,trace);
+        // Also do any following projections, which are not in the local schedule otherwise
+        if( n instanceof MultiNode )
+            for( Node use : n._outputs )
+                step(use,trace);
+    }
+
+    // From here down shamelessly copied from Evaluator, written by @Xmilia
+    private static Object compute( Node n ) {
+        return switch( n ) {
+        case AddFNode     adf  -> d(adf.in(1)) +  d(adf.in(2));
+        case AddNode      add  -> x(add.in(1)) +  x(add.in(2));
+        case AndNode      and  -> x(and.in(1)) &  x(and.in(2));
+        case BoolNode.EQF eqf  -> d(eqf.in(1)) == d(eqf.in(2)) ? 1L : 0L;
+        case BoolNode.LEF lef  -> d(lef.in(1)) <= d(lef.in(2)) ? 1L : 0L;
+        case BoolNode.LTF ltf  -> d(ltf.in(1)) <  d(ltf.in(2)) ? 1L : 0L;
+        case BoolNode.EQ  eq   -> Objects.equals(val(eq.in(1)), val(eq.in(2))) ? 1L : 0L; // Bool EQ supports pointers, nil, and integers
+        case BoolNode.LE  le   -> x(le .in(1)) <= x(le .in(2)) ? 1L : 0L;
+        case BoolNode.LT  lt   -> x(lt .in(1)) <  x(lt .in(2)) ? 1L : 0L;
+        case CastNode    cast  -> val(cast.in(1));
+        case ConstantNode con  -> con(con._con);
+        case DivFNode     dvf  -> d(dvf.in(2))==0 ? 0D : d(dvf.in(1)) /  d(dvf.in(2));
+        case DivNode      div  -> x(div.in(2))==0 ? 0L : x(div.in(1)) /  x(div.in(2));
+        case LoadNode     ld   -> load(ld);
+        case MinusFNode   mnf  -> - d(mnf.in(1));
+        case MinusNode    sub  -> - x(sub.in(1));
+        case MulFNode     mlf  -> d(mlf.in(1)) *  d(mlf.in(2));
+        case MulNode      mul  -> x(mul.in(1)) *  x(mul.in(2));
+        case NewNode      alloc-> alloc(alloc);
+        case NotNode      not  -> x(not.in(1)) == 0 ? 1L : 0L;
+        case OrNode       or   -> x(or .in(1)) |  x(or .in(2));
+        case ProjNode     proj -> proj._type instanceof TypeMem ? "$mem" : val(proj.in(0));
+        case ReadOnlyNode read -> val(read.in(1));
+        case SarNode      sar  -> x(sar.in(1)) >> x(sar.in(2));
+        case MemMergeNode merge-> "$mem";
+        case ShlNode      shl  -> x(shl.in(1)) << x(shl.in(2));
+        case ShrNode      shr  -> x(shr.in(1)) >>>x(shr.in(2));
+        case StoreNode    st   -> store(st);
+        case SubNode      sub  -> x(sub.in(1)) -  x(sub.in(2));
+        case SubFNode     sbf  -> d(sbf.in(1)) -  d(sbf.in(2));
+        case ToFloatNode  toflt-> (double)x(toflt.in(1));
+        case XorNode      xor  -> x(xor.in(1)) ^  x(xor.in(2));
+        default -> throw Utils.TODO();
+        };
+    }
+
+    // Fetch without unboxing, searching up-Frame
+    static Object val( Node n ) { return F.get(n); }
+    // Fetch and unbox as primitive long
+    static long   x( Node n ) { Object d = F.get(n); return d==null ? 0 : (Long)  F.get(n);  }
+    // Fetch and unbox as primitive double
+    static double d( Node n ) { Object d = F.get(n); return d==null ? 0 : (Double)F.get(n);  }
+    // Fetch and unbox a function constant
+    static TypeFunPtr tfp(Node n) { return (TypeFunPtr)F.get(n); }
+    // Fetch and unbox a closure
+    static Closure clj(Node n) { return (Closure)F.get(n); }
+
+    // Java box ints and floats.  Other things can just be null or some informative string
+    private static Object con( Type t ) {
+        return switch ( t ) {
+        case TypeInteger i -> i.isConstant() ? (Long  )i.value() : "INT";
+        case TypeFloat   f -> f.isConstant() ? (Double)f.value() : "FLT";
+        case TypeMemPtr tmp -> tmp;
+        case TypeFunPtr tfp -> tfp;
+        case TypeMem mem -> "MEM";
+        default -> null;
+        };
+    }
+
+    // Convert array size to array element count
+    private static int offToIdx( long off, TypeStruct t) {
+        off -= t.aryBase();
+        int scale = t.aryScale();
+        long mask = (1L << scale)-1;
+        assert (off & mask) == 0;
+        return (int)(off>>scale);
+    }
+
+    // Builds and returns a pointer Object
+    private static Object alloc(NewNode alloc) {
+        TypeStruct type = alloc._ptr._obj;
+        if( type.isAry() ) {
+            long sz = (Long)val(alloc.in(1));
+            long x = offToIdx(sz, type);
+            int n = (int)x;
+            if( n!=x || n<0 )
+                throw new NegativeArraySizeException(""+n);
+            Object[] ary = new Object[n]; // Array body
+            var elem = type._fields[1]._type;
+            if (elem instanceof TypeInteger) {
+                Arrays.fill( ary, 0L );
+            } else if (elem instanceof TypeFloat) {
+                Arrays.fill( ary, 0D );
+            } else {
+                assert elem instanceof TypeMemPtr || elem instanceof TypeFunPtr;
+            }
+            return ary;
+        }
+
+        int num = type._fields.length;
+        Object[] ptr = new Object[num];
+        for( int i=0; i<num; i++ )
+            ptr[i] = con(type._fields[i]._type.makeZero());
+        return ptr;
+    }
+
+    private static Object load( LoadNode ld ) {
+        TypeMemPtr tmp = (TypeMemPtr)ld.ptr()._type;
+        Object[] fs = (Object[])val(ld.ptr());
+        if( ld._name.equals("#") )
+            return (long)fs.length;
+        int idx = tmp._obj.isAry()
+            ? offToIdx(x(ld.off()),tmp._obj)
+            : tmp._obj.find(ld._name);
+        return fs[idx];
+    }
+
+    private static Object store( StoreNode st ) {
+        if( st._name.equals("#") )
+            return "$mem";      // Eval stores the length in the java object[], no need to set it now
+        TypeMemPtr tmp = (TypeMemPtr)st.ptr()._type;
+        Object[] fs = (Object[])val(st.ptr());
+        int idx = tmp._obj.isAry()
+            ? offToIdx(x(st.off()),tmp._obj)
+            : tmp._obj.find(st._name);
+        Object val = val(st.val());
+        fs[idx] = val;
+        return "$mem";
+    }
+
+
+    // ------------------------------------------------------------------------
+    private static final IdentityHashMap<Object,Object> VISIT = new IdentityHashMap<>();
+
+
+    static void traceCtrl( CFGNode BB, SB sb ) {
+        if( sb==null ) return;
+        IRPrinter.printLine(BB,sb.p("--- "));
+        System.out.print(sb);
+        sb.clear();
+    }
+    static void traceData( Node n, SB sb ) {
+        if( sb==null ) return;
+        IRPrinter.printLine(n,sb).unchar();
+        _print( n._type, F.get(n), sb.p('\t'), VISIT );
+        System.out.println(sb);
+        sb.clear();
+        VISIT.clear();
+    }
+
+    // Use type to print x as a string.  Uses a new VISIT table so the debugger
+    // doesn't try to reuse VISIT if stopping mid-print.  The trace code reuses
+    // VISIT endlessly for some minor speed hope
+    static String prettyPrint( Type t, Object x ) { return _print(t,x,new SB(), new IdentityHashMap<>()).toString(); }
+    static SB _print( Type t, Object x, SB sb, IdentityHashMap<Object,Object> visit ) {
+        if( x instanceof String s ) return sb.p(s);
+        if( x == null ) return sb.p("null");
+        return switch( t ) {
+        case TypeInteger i -> sb.p(  (Long)x);
+        case TypeFloat   f -> sb.p((Double)x);
+        case TypeMemPtr tmp -> {
+            if( visit.containsKey(x) ) yield sb.p("$cyclic");
+            visit.put(x,x);
+            // Since never can close the type cycle, without cyclic types, have
+            // to handle FRefs even here
+            if( tmp.isFRef() )
+                tmp = tmp.makeFrom(((TypeMemPtr)Parser.TYPES.get(tmp._obj._name))._obj);
+
+            Object[] xs = (Object[])x; // Array of fields
+            if( tmp._obj.isAry() ) {
+                Type elem = tmp._obj._fields[1]._type;
+                if( elem == TypeInteger.U8 ) {
+                    // Shortcut u8[] as a String
+                    for( Object o : xs )
+                        sb.p((char)(long)(Long)o);
+                } else {
+                    // Array of elements
+                    elem.print(sb).p("[ ");
+                    for( Object o : xs )
+                        _print( elem, o, sb, visit ).p( "," );
+                    sb.unchar().p("]");
+                }
+            } else {
+                sb.p(tmp._obj._name).p("{");
+                Field[] flds = tmp._obj._fields;
+                for( int i=0; i<flds.length; i++ )
+                    _print( flds[i]._type,xs[i], sb.p(flds[i]._fname).p("="), visit ).p(",");
+                sb.unchar().p("}");
+            }
+            yield sb;
+        }
+        case TypeFunPtr tfp -> sb.p(x.toString());
+        case TypeRPC rpc -> sb.p(x.toString());
+        case TypeMem mem -> sb.p("$mem");
+        case TypeTuple tt -> {
+            if( tt._types.length>1 && tt._types[1] instanceof TypeMemPtr )
+                // Assume a NewNode
+                yield _print( tt._types[1], x, sb, visit );
+            throw Utils.TODO();
+        }
+        case Type tt -> {
+            if( tt == Type.NIL ) yield sb.p("null");
+            throw Utils.TODO();
+        }
+        };
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/FuzzerWrap.java b/chapter20/src/test/java/com/seaofnodes/simple/FuzzerWrap.java
new file mode 100644
index 00000000..d67b2065
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/FuzzerWrap.java
@@ -0,0 +1,43 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.fuzzer.Fuzzer;
+import java.util.Random;
+import org.junit.Ignore;
+import org.junit.Test;
+import static org.junit.Assert.assertTrue;
+
+/**
+ * To use the fuzzer run the <code>fuzzPeeps</code> methods.
+ * This can be done from IntelliJ Gui or remove the `@Ignore` annotation and start the test case from the command line
+ * via <code>mvn clean test -Dtest=com.seaofnodes.simple.Fuzzer08Test#fuzzPeeps</code>
+ */
+public class FuzzerWrap {
+
+    @Ignore
+    @Test
+    public void fuzzPeeps() {
+        var fuzzer = new Fuzzer();
+        for (int i=0; i<1000000; i++)
+            fuzzer.fuzzPeeps(i);
+        assertTrue(fuzzer.noExceptions());
+    }
+
+
+    @Test
+    public void fuzzPeepsSmall() {
+        Random R = new Random(System.currentTimeMillis());
+        var fuzzer = new Fuzzer();
+        for (int i=0; i<100; i++)
+            fuzzer.fuzzPeeps( R.nextLong());
+        assertTrue(fuzzer.noExceptions());
+    }
+
+    @Test
+    @Ignore
+    public void fuzzPeepTiming() {
+        var fuzzer = new Fuzzer();
+        int max_nid=0;
+        for (int i=0; i<1000000; i++)
+            max_nid = fuzzer.fuzzPeepTiming(i, max_nid);
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/Main.java b/chapter20/src/test/java/com/seaofnodes/simple/Main.java
new file mode 100644
index 00000000..523bd306
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/Main.java
@@ -0,0 +1,17 @@
+package com.seaofnodes.simple;
+
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+public class Main {
+    // Compile and run a simple program
+    public static void main( String[] args ) throws Exception {
+        // First arg is file, 2nd+ args are program args
+        String src = Files.readString(Path.of(args[0]));
+        int arg = Integer.valueOf(args[1]);
+        CodeGen code = new CodeGen(src);
+        code.parse().opto().typeCheck().GCM().localSched();
+        System.out.println(code._stop);
+        System.out.println(Eval2.eval(code,arg,100000));
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/MergeSortTest.java b/chapter20/src/test/java/com/seaofnodes/simple/MergeSortTest.java
new file mode 100644
index 00000000..d48449d5
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/MergeSortTest.java
@@ -0,0 +1,65 @@
+package com.seaofnodes.simple;
+
+import org.junit.Test;
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.fail;
+
+public class MergeSortTest {
+
+    @Test
+    public void testMergeSort() {
+        CodeGen code = new CodeGen(
+"""
+// based on the top-down version from https://en.wikipedia.org/wiki/Merge_sort
+
+val merge_sort = { int[] a, int[] b, int n ->
+    copy_array(a, 0, n, b);
+    split_merge(a, 0, n, b);
+};
+
+val split_merge = { int[] b, int begin, int end, int[] a ->
+    if (end - begin <= 1)
+        return 0;
+    int middle = (end + begin) / 2;
+    split_merge(a, begin, middle, b);
+    split_merge(a, middle, end, b);
+    merge(b, begin, middle, end, a);
+    return 0;
+};
+
+val merge = { int[] b, int begin, int middle, int end, int[] a ->
+    int i = begin, j = middle;
+
+    for (int k = begin; k < end; k++) {
+        // && and ||
+        bool cond = false;
+        if (i < middle) {
+            if (j >= end)          cond = true;
+            else if (a[i] <= a[j]) cond = true;
+        }
+        if (cond) b[k] = a[i++];
+        else      b[k] = a[j++];
+    }
+};
+
+val copy_array = { int[] a, int begin, int end, int[] b ->
+    for (int k = begin; k < end; k++)
+        b[k] = a[k];
+};
+
+int[] !a = new int[arg];
+int[] !b = new int[a#];
+
+for (int i = 0; i < a#; i++)
+    a[i] = a# - i;
+
+merge_sort(a, b, a#);
+
+return a;
+""");
+        code.parse().opto();
+        assertEquals("Stop[ return [int]; return 0; ]", code._stop.toString());
+        assertEquals("int[ 1,2,3,4,5,6,7,8,9,10,11]", Eval2.eval(code, 11));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/SchedulerTest.java b/chapter20/src/test/java/com/seaofnodes/simple/SchedulerTest.java
new file mode 100644
index 00000000..d50c302a
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/SchedulerTest.java
@@ -0,0 +1,73 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.evaluator.Evaluator;
+import com.seaofnodes.simple.node.StopNode;
+import org.junit.Assert;
+import org.junit.Ignore;
+import org.junit.Test;
+
+import static org.junit.Assert.assertEquals;
+
+public class SchedulerTest {
+
+    private static void assertObj(Object obj, String name, Object... fields) {
+        assertEquals(Evaluator.Obj.class, obj.getClass());
+        var o = (Evaluator.Obj)obj;
+        assertEquals(name, o.struct()._name);
+        Assert.assertArrayEquals(fields, o.fields());
+    }
+
+    @Test
+    @Ignore
+    public void testJig() {
+        CodeGen code = new CodeGen("""
+struct S {
+    int f;
+}
+S !v=new S;
+v.f = 2;
+int i=v.f;
+if (arg) v.f=1;
+return i;
+""");
+        code.parse();//.opto();
+        var eval = new Evaluator(code._stop);
+        assertEquals(2L, eval.evaluate(1, 10));
+    }
+
+    @Test
+    public void testStoreInIf() {
+        CodeGen code = new CodeGen("""
+struct S {
+    int f;
+};
+S !v0=new S;
+if(arg) v0.f=1;
+return v0;
+""");
+        code.parse().opto();
+        var eval = new Evaluator(code._stop);
+        assertObj(eval.evaluate(0, 10), "S", 0L);
+        assertObj(eval.evaluate(1, 10), "S", 1L);
+    }
+
+    @Test
+    public void testStoreInIf2() {
+        CodeGen code = new CodeGen("""
+struct S {
+    int f;
+};
+S !v=new S;
+v.f = 2;
+int i=new S.f;
+i=v.f;
+if (arg) v.f=1;
+return i;
+""");
+        code.parse().opto();
+        var eval = new Evaluator(code._stop);
+        assertEquals(2L, eval.evaluate(0, 10));
+        assertEquals(2L, eval.evaluate(1, 10));
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/TypeTest.java b/chapter20/src/test/java/com/seaofnodes/simple/TypeTest.java
new file mode 100644
index 00000000..d94f5b5a
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/TypeTest.java
@@ -0,0 +1,158 @@
+package com.seaofnodes.simple;
+
+import com.seaofnodes.simple.type.*;
+import org.junit.Assert;
+import org.junit.Test;
+import static org.junit.Assert.assertSame;
+
+public class TypeTest {
+
+    // Test basic properties and GLB
+    @Test
+    public void testTypeAdHoc() {
+        Assert.assertEquals( Type.BOTTOM, TypeInteger.TRUE.meet(TypeNil.NIL) );
+        Assert.assertEquals( Type.BOTTOM, TypeInteger.TOP.meet(TypeNil.NIL) );
+
+
+        TypeStruct s1 = TypeStruct.make("s1", new Field[]{
+                Field.make("a", TypeInteger.BOT,-1, false),
+                Field.make("b", TypeInteger.BOT,-2, false) });
+        TypeStruct s2 = TypeStruct.make("s2", new Field[]{
+                Field.make("a", TypeInteger.BOT,-3, false),
+                Field.make("b", TypeInteger.BOT,-4, false) });
+        Assert.assertEquals(s1.makeRO(), s1.glb());
+        Assert.assertNotEquals(s1, s1.dual());
+        Assert.assertEquals(s1.makeRO(), s1.dual().glb());
+
+        TypeMem m1 = TypeMem.make(1,TypeNil.NIL);
+        TypeMem m2 = TypeMem.make(2,TypeInteger.U16);
+        TypeMem m3 = TypeMem.make(3,TypeFloat.F64);
+        TypeMem m4 = TypeMem.make(4,TypeInteger.BOT);
+
+        Assert.assertNotEquals(m1, m2);
+        Assert.assertNotEquals(m2, m3);
+        Assert.assertNotEquals(m3, m4);
+
+        Assert.assertEquals(TypeStruct.BOT, s1.meet(s2));
+        Assert.assertEquals(TypeMem   .BOT, m1.meet(m2));
+        Assert.assertEquals(TypeMem.make(0,Type.BOTTOM), m1.meet(m3));
+        Assert.assertEquals(TypeMem   .BOT, m3.meet(m4));
+
+        Assert.assertEquals(TypeMem.make(1,Type.BOTTOM), m1.glb());
+        Assert.assertEquals(TypeMem.make(1,Type.XNIL), m1.dual());
+        Assert.assertEquals(m4.dual(), m4.glb().dual());
+
+        TypeMemPtr ptr1 = TypeMemPtr.make(s1);
+        Assert.assertEquals(s1, ptr1._obj);
+        TypeMemPtr ptr2 = TypeMemPtr.make(s2);
+        Assert.assertEquals(s2, ptr2._obj);
+
+        TypeMemPtr ptr1nil = TypeMemPtr.makeNullable(s1);
+        Assert.assertEquals(s1, ptr1nil._obj);
+        Assert.assertTrue( ptr1nil.nullable() );
+        Assert.assertNotNull( ptr1nil._obj );
+        TypeMemPtr ptr2nil = TypeMemPtr.makeNullable( s2);
+        Assert.assertEquals(s2, ptr2nil._obj);
+
+        Assert.assertNotEquals(ptr1, ptr2);
+        Assert.assertNotEquals(ptr1, ptr1.glb());
+        Assert.assertEquals(ptr1nil.makeRO(), ptr1.glb());
+
+        Assert.assertEquals(ptr1, ptr1.dual().dual());
+        Assert.assertEquals(ptr1.glb().makeRO(), ptr1.dual().glb());
+        Assert.assertEquals(TypeMemPtr.makeNullable(TypeStruct.BOT), ptr1.meet(ptr2nil));
+        Assert.assertEquals(ptr1.glb(), ptr1.meet(TypeNil.NIL).makeRO());
+
+        TypeMemPtr TOP = TypeMemPtr.TOP;
+        TypeMemPtr BOT = TypeMemPtr.makeNullable(TypeStruct.BOT);
+        TypeMemPtr PTR = TypeMemPtr.make(TypeStruct.BOT);
+        Type NULL = TypeNil.NIL;
+        Type PTR_meet_NULL = NULL.meet(PTR);
+        Assert.assertEquals(BOT, PTR_meet_NULL);
+        Type ptr1_meet_ptr2 = ptr1.meet(ptr2);
+        Assert.assertEquals(PTR, ptr1_meet_ptr2);
+        Type NULL_join_ptr1 = NULL.join(ptr1);
+        Assert.assertEquals(TypePtr.XNPTR, NULL_join_ptr1);
+        Type NULL_join_PTR = PTR.join(NULL);
+        Assert.assertEquals(TypePtr.XNPTR, NULL_join_PTR);
+        Type ptr1_dual = ptr1.dual();
+        Type nullableptr1_dual = ptr1nil.dual();
+    }
+
+    // Test theoretical properties.
+    // This is a symmetric complete bounded (ranked) lattice.
+    // Also, the meet is commutative and associative.
+    // The lattice has a dual (symmetric), and join is ~(~x meet ~y).
+    // See https://en.wikipedia.org/wiki/Lattice_(order).
+    @Test
+    public void testLatticeTheory() {
+        Type[] ts = Type.gather();
+
+        // Confirm commutative & complete
+        for( Type t0 : ts )
+            for( Type t1 : ts ) {
+                check_commute  (t0,t1);
+                check_symmetric(t0,t1);
+            }
+
+        // Confirm associative
+        for( Type t0 : ts )
+            for( Type t1 : ts )
+                for( Type t2 : ts )
+                    assoc(t0,t1,t2);
+
+        // Confirm symmetry.  If A isa B, then A.join(C) isa B.join(C)
+        for( Type t0 : ts )
+            for( Type t1 : ts )
+                if( t0.isa(t1) )
+                    for( Type t2 : ts ) {
+                        Type t02 = t0.join(t2);
+                        Type t12 = t1.join(t2);
+                        Type mt  = t02.meet(t12);
+                        assertSame(mt,t12);
+                    }
+    }
+
+    // By design in meet, args are already flipped to order _type, which forces
+    // symmetry for things with badly ordered _type fields.  The question is
+    // still interesting for other orders.
+    private static void check_commute( Type t0, Type t1 ) {
+        if( t0==t1 ) return;
+        if( t0.is_simple() && !t1.is_simple() ) return; // By design, flipped the only allowed order
+        Type mta = t0.meet(t1);
+        Type mtb = t1.meet(t0); // Reverse args and try again
+        assertSame(mta,mtb);
+    }
+
+    // A & B = MT
+    // Expect: ~A & ~MT == ~A
+    // Expect: ~B & ~MT == ~B
+    private static void check_symmetric( Type t0, Type t1 ) {
+        if( t1==t0 ) return;
+        Type mt = t0.meet(t1);
+        Type dm = mt.dual();
+        Type d0 = t0.dual();
+        Type d1 = t1.dual();
+        Type ta = dm.meet(d1);
+        Type tb = dm.meet(d0);
+        assertSame(ta,d1);
+        assertSame(tb,d0);
+    }
+
+    private static void assoc( Type t0, Type t1, Type t2 ) {
+        Type t01   = t0 .meet(t1 );
+        Type t12   = t1 .meet(t2 );
+        Type t01_2 = t01.meet(t2 );
+        Type t0_12 = t0 .meet(t12);
+        assertSame(t01_2,t0_12);
+    }
+
+    // Test cyclic types and meets
+    @Test
+    public void testCyclic0() {
+        Type d0 = TypeStruct.S1.dual();
+        Type d1 = d0.dual();
+        assertSame(TypeStruct.S1,d1);
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Evaluator.java b/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Evaluator.java
new file mode 100644
index 00000000..a3b87e90
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Evaluator.java
@@ -0,0 +1,383 @@
+package com.seaofnodes.simple.evaluator;
+
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.*;
+
+import java.util.*;
+
+public class Evaluator {
+
+    private static final Object MEMORY = new Object();
+
+    public record Obj(TypeStruct struct, Object[] fields) {
+        private void init(IdentityHashMap<Obj, Integer> objs) {
+            var oid = objs.get(this);
+            if (oid != null) {
+                if (oid != 0) objs.put(this, 0);
+                return;
+            }
+            objs.put(this, -1);
+            for (var obj : fields) {
+                if (obj instanceof Obj o) o.init(objs);
+            }
+        }
+        private static int p(StringBuilder sb, IdentityHashMap<Obj, Integer> objs, int id, String indentation, String step, String sep, Object obj) {
+            if (obj instanceof Obj o) return o.p(sb, objs, id, indentation, step, sep);
+            sb.append(obj);
+            return id;
+        }
+        private int p(StringBuilder sb, IdentityHashMap<Obj, Integer> objs, int id, String indentation, String step, String sep) {
+            var cid = objs.get(this);
+            assert cid != null;
+            if (cid > 0) {
+                sb.append("obj@").append(cid);
+                return id;
+            }
+            if (struct._name.equals("[u8]")) {
+                sb.append('"');
+                for (int i=struct._fields.length-1; i<fields.length; i++) {
+                    var v = fields[i];
+                    if (v == null) v = 0;
+                    assert v instanceof Number;
+                    var n = ((Number)v).byteValue() & 0xFF;
+                    if (n >= 0x20 && n < 0x80) {
+                        if (n == 0x22 || n == 0x5C) sb.append("\\");
+                        sb.append((char)n);
+                    } else {
+                        sb.append("\\x").append("0123456789abcdef".charAt(n >> 4)).append("0123456789abcdef".charAt(n & 0xF));
+                    }
+                }
+                sb.append('"');
+                return id;
+            }
+            sb.append("Obj<").append(struct._name).append(">");
+            if (cid == 0) {
+                cid = id++;
+                objs.put(this, cid);
+                sb.append("@").append(cid);
+            }
+            sb.append("{");
+            if (struct._fields.length == 0) {
+                assert !struct.isAry();
+                sb.append("}");
+                return id;
+            }
+            String nextIndent = indentation + step;
+            int e = struct._fields.length - 1;
+            for(int i=0; i<e; i++) {
+                sb.append(nextIndent).append(struct._fields[i]._fname).append("=");
+                id = p(sb, objs, id, nextIndent, step, sep, fields[i]);
+                sb.append(sep);
+            }
+            sb.append(nextIndent).append(struct._fields[e]._fname).append("=");
+            if (struct.isAry()) {
+                sb.append("[");
+                if (fields.length > e) {
+                    String innerIndent = nextIndent + step;
+                    sb.append(innerIndent);
+                    id = p(sb, objs, id, nextIndent, step, sep, fields[e]);
+                    for (int i = e+1; i < fields.length; i++) {
+                        sb.append(sep).append(innerIndent);
+                        id = p(sb, objs, id, nextIndent, step, sep, fields[i]);
+                    }
+                    sb.append(nextIndent);
+                }
+                sb.append("]");
+            } else {
+                id = p(sb, objs, id, nextIndent, step, sep, fields[e]);
+            }
+            sb.append(indentation).append("}");
+            return id;
+        }
+        private StringBuilder p(StringBuilder sb, String indentation, String step, String sep) {
+            var objs = new IdentityHashMap<Obj, Integer>();
+            init(objs);
+            p(sb, objs, 1, indentation, step, sep);
+            return sb;
+        }
+        @Override
+        public String toString() {
+            if (struct._name.equals("[u8]")) {
+                var sb = new StringBuilder();
+                for (int i=struct._fields.length-1; i<fields.length; i++) {
+                    var v = fields[i];
+                    if (v == null) v = 0;
+                    assert v instanceof Number;
+                    var n = ((Number)v).byteValue() & 0xFF;
+                    sb.append((char)n);
+                }
+                return sb.toString();
+            }
+            return p(new StringBuilder(), "", "", ",").toString();
+        }
+        public String pretty() {
+            return p(new StringBuilder(), "\n", "  ", "").toString();
+        }
+    }
+
+    private static int getFieldIndex(TypeStruct struct, MemOpNode memop, long off) {
+        int idx = struct.find(memop._name);
+        if( idx >= 0 ) return idx;
+        throw new AssertionError("Field "+memop._name+" not found in struct " + struct._name);
+    }
+
+    public enum Status {
+        TIMEOUT,
+        FALLTHROUGH
+    }
+
+    /**
+     * Find the start node from some node in the graph or null if there is no start node
+     */
+    private static StartNode findStart(BitSet visit, Node node) {
+        if (node == null) return null;
+        if( visit.get(node._nid) ) return null;
+        visit.set(node._nid);
+        StartNode start = node instanceof StartNode ? (StartNode) node : null;
+        for( Node def : node._inputs ) {
+            var res = findStart(visit,def);
+            if( res != null ) start = res;
+        }
+        for( Node use : node._outputs ) {
+            var res = findStart(visit,use);
+            if( res != null ) start = res;
+        }
+        return start;
+    }
+
+    private final Object[] values;
+    private final ArrayList<Object> phiCache = new ArrayList<>();
+    private final StartNode start;
+    private final Scheduler.Block startBlock;
+
+    public Evaluator(Node graph) {
+        var visited = new BitSet();
+        this.start = findStart(visited, graph);
+        if (this.start == null) {
+            this.values = null;
+            this.startBlock = null;
+            return;
+        }
+        this.startBlock = Scheduler.schedule(this.start);
+        this.values = new Object[visited.length()];
+    }
+
+    private long div(DivNode div) {
+        long in2 = vall(div.in(2));
+        return in2 == 0 ? 0 : vall(div.in(1)) / in2;
+    }
+    private double div(DivFNode div) {
+        double in2 = vald(div.in(2));
+        return in2 == 0 ? 0 : vald(div.in(1)) / in2;
+    }
+
+    private static long offToIdx(long off, TypeStruct t) {
+        off -= t.aryBase();
+        int scale = t.aryScale();
+        long mask = (1L << scale)-1;
+        assert (off & mask) == 0;
+        return off>>scale;
+    }
+
+    private Object alloc(NewNode alloc) {
+        TypeStruct type = alloc._ptr._obj;
+        Object[] body=null;
+        int num;
+        if( type.isAry() ) {
+            long sz = (Long)val(alloc.in(1));
+            long n = offToIdx(sz, type);
+            if( n < 0 )
+                throw new NegativeArraySizeException(""+n);
+            body = new Object[(int)n+1]; // Array body
+            var elem = type._fields[1]._type;
+            if (elem instanceof TypeInteger) {
+                for (int i=0; i<n; i++) body[i+1] = 0L;
+            } else if (elem instanceof TypeFloat) {
+                for (int i = 0; i < n; i++) body[i+1] = 0D;
+            } else {
+                assert elem instanceof TypeMemPtr;
+            }
+            // Length value
+            body[0] = vall(alloc.in(2+2));
+        } else {
+            body = new Object[num = type._fields.length];
+            for( int i=0; i<num; i++ )
+                body[i] = switch( alloc._ptr._obj._fields[i]._type ) {
+                case TypeInteger ti -> 0L;
+                case TypeFloat tf -> 0;
+                default -> null;
+                };
+        }
+        Object[] mems = new Object[type._fields.length+2];
+        // mems[0] is control
+        mems[1] = new Obj(type,body); // the ref
+        // mems[2+...] are memory aliases
+        return mems;
+    }
+
+    private Object load(LoadNode load) {
+        var from = (Obj)val(load.ptr());
+        var off = vall(load.off());
+        var idx = getFieldIndex(from.struct, load, (Long)off);
+        if( idx==from.struct._fields.length-1 && from.struct.isAry() ) {
+            long len = from.fields.length - from.struct._fields.length + 1;
+            long i = offToIdx(off, from.struct);
+            if( i < 0 || i >= len )
+                throw new ArrayIndexOutOfBoundsException("Array index out of bounds " + i + " < " + len);
+            return from.fields[(int)i+from.struct._fields.length-1];
+
+        } else
+            return from.fields[idx];
+    }
+
+    private Object store(StoreNode store) {
+        var to = (Obj)val(store.ptr());
+        var off = vall(store.off());
+        var val = val(store.val());
+        var idx = getFieldIndex(to.struct, store, (Long)off);
+        if( idx==to.struct._fields.length-1 && to.struct.isAry() ) {
+            long len = to.fields.length - to.struct._fields.length + 1;
+            long i = offToIdx(off, to.struct);
+            if( i < 0 || i >= len )
+                throw new RuntimeException("Array index out of bounds " + off + " <= " + len);
+            to.fields[(int)i+to.struct._fields.length-1] = val;
+        } else
+            to.fields[idx] = val;
+        return null;
+    }
+
+    private static boolean isTrue(Object obj) {
+        if (obj == null) return false;
+        if (obj instanceof Number n) return n.longValue() != 0;
+        return true;
+    }
+
+    private Object val(Node node) {
+        return values[node._nid];
+    }
+
+    private long vall(Node node) {
+        var v = val(node);
+        if (v instanceof Number n) return n.longValue();
+        throw new AssertionError("Not a long " + v);
+    }
+    private double vald(Node node) {
+        var v = val(node);
+        if (v instanceof Number n) return n.doubleValue();
+        if( v == null ) return 0;
+        throw new AssertionError("Not a double " + v);
+    }
+
+    private Object cons(ConstantNode cons) {
+        var type = cons.compute();
+        if (type instanceof TypeInteger i) return i.isConstant() ? i.value() : Integer.MAX_VALUE;
+        if (type instanceof TypeFloat i) return i.value();
+        return null;
+    }
+
+    private Object exec(Node node) {
+        return switch (node) {
+            case ConstantNode cons  -> cons(cons);
+            case AddNode      add   -> vall(add.in(1)) + vall(add.in(2));
+            case AddFNode     add   -> vald(add.in(1)) + vald(add.in(2));
+            case BoolNode.EQF eq    -> vald(eq.in(1)) == vald(eq.in(2)) ? 1L : 0L;
+            case BoolNode.LEF le    -> vald(le.in(1)) <= vald(le.in(2)) ? 1L : 0L;
+            case BoolNode.LTF lt    -> vald(lt.in(1)) <  vald(lt.in(2)) ? 1L : 0L;
+            case BoolNode.EQ  eq    -> Objects.equals(val(eq.in(1)), val(eq.in(2))) ? 1L : 0L;
+            case BoolNode.LE  le    -> vall(le.in(1)) <= vall(le.in(2)) ? 1L : 0L;
+            case BoolNode.LT  lt    -> vall(lt.in(1)) <  vall(lt.in(2)) ? 1L : 0L;
+            case DivNode      div   -> div(div);
+            case DivFNode     div   -> div(div);
+            case MinusNode    minus -> -vall(minus.in(1));
+            case MinusFNode   minus -> -vald(minus.in(1));
+            case MulNode      mul   -> vall(mul.in(1)) * vall(mul.in(2));
+            case MulFNode     mul   -> vald(mul.in(1)) * vald(mul.in(2));
+            case NotNode      not   -> isTrue(val(not.in(1))) ? 0L : 1L;
+            case SubNode      sub   -> vall(sub.in(1)) - vall(sub.in(2));
+            case SubFNode     sub   -> vald(sub.in(1)) - vald(sub.in(2));
+            case ShlNode      shl   -> vall(shl.in(1)) << vall(shl.in(2));
+            case ShrNode      shr   -> vall(shr.in(1)) >>> vall(shr.in(2));
+            case SarNode      sar   -> vall(sar.in(1)) >> vall(sar.in(2));
+            case AndNode      and   -> vall(and.in(1)) & vall(and.in(2));
+            case  OrNode      or    -> vall(or .in(1)) | vall(or .in(2));
+            case XorNode      xor   -> vall(xor.in(1)) ^ vall(xor.in(2));
+            case CastNode     cast  -> val(cast.in(1));
+            case ToFloatNode  cast  -> (double)vall(cast.in(1));
+            case LoadNode     load  -> load(load);
+            case StoreNode    store -> store(store);
+            case NewNode      alloc -> alloc(alloc);
+            case CProjNode    cproj -> ((Object[])val(cproj.ctrl()))[cproj._idx];
+            case ProjNode     proj  -> ((Object[])val( proj.in(0) ))[ proj._idx];
+            case MemMergeNode mem   -> null;
+            case ReadOnlyNode ro    -> val(ro.in(1));
+            case CallNode     call  -> Utils.TODO(); // should not reach here, go the IfNode route
+            default                 -> throw new AssertionError("Unexpected node " + node);
+        };
+    }
+
+    /**
+     * Run the graph until either a return is found or the number of loop iterations are done.
+     */
+    public Object evaluate(long parameter, int loops) {
+        if (start == null) return Status.TIMEOUT;
+        var s = new Object[start.compute()._types.length];
+        s[1] = MEMORY;
+        s[2] = parameter;
+        values[start._nid] = s;
+        int i=0;
+        Scheduler.Block block = this.startBlock;
+        for(;;) {
+            for(; i<block.nodes().length;i++) values[block.nodes()[i]._nid] = exec(block.nodes()[i]);
+            i=0;
+            switch (block.exit()) {
+            case null:
+                return Status.FALLTHROUGH;
+            case ReturnNode ret :  return val(ret .expr());
+            case IfNode ifn:
+                block = block.next()[isTrue(val(ifn.in(1))) ? 0 : 1];
+                if (block == null) return Status.FALLTHROUGH;
+                break;
+            case RegionNode region:
+                if (loops-- <= 0) return Status.TIMEOUT;
+                int exit = block.exitId();
+                assert exit > 0 && region.nIns() > exit;
+                block = block.next()[0];
+                assert block != null;
+                for (; i < block.nodes().length; i++) {
+                    if (!(block.nodes()[i] instanceof PhiNode phi)) break;
+                    var val = region instanceof FunNode fun && "main".equals(fun._name) && ((ParmNode)phi)._idx==2 && exit==1
+                            ? parameter
+                            : val(phi.in(exit));
+                    phiCache.add(val);
+                }
+                for (i=0; i<phiCache.size(); i++) {
+                    values[block.nodes()[i]._nid] = phiCache.get(i);
+                }
+                phiCache.clear();
+                break;
+            default:
+                throw Utils.TODO("Unexpected control node " + block.exit());
+            }
+        }
+    }
+
+    public static Object evaluate(StopNode graph) {
+        return evaluate(graph, 0);
+    }
+
+    public static Object evaluate(StopNode graph, long parameter) {
+        return evaluate(graph, parameter, 1000);
+    }
+
+    public static Object evaluate(StopNode graph, long parameter, int loops) {
+        var res = evaluateWithResult(graph, parameter, loops);
+        if (res == Status.TIMEOUT) throw new RuntimeException("Timeout");
+        return res;
+    }
+
+    public static Object evaluateWithResult(StopNode graph, long parameter, int loops) {
+        return new Evaluator(graph).evaluate(parameter, loops);
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Scheduler.java b/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Scheduler.java
new file mode 100644
index 00000000..4bfa7628
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/evaluator/Scheduler.java
@@ -0,0 +1,606 @@
+package com.seaofnodes.simple.evaluator;
+
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.node.*;
+import com.seaofnodes.simple.type.Type;
+
+import java.util.*;
+
+/**
+ * A late scheduler for test cases.
+ * <br>
+ * <br>
+ * This scheduler is used for tests and is not the final scheduler.
+ * <br>
+ * <br>
+ * The scheduler schedules not as late as possible. Since it is just for test cases this is fine.
+ * A better scheduler will try to place nodes outside of loops. Due to the schedule late strategy
+ * this scheduler might place initialization code in loops.
+ * <br>
+ * We schedule late here since memory edges have some implicit information. There can only be one
+ * memory edge (for a field) at a time. However, before <code>if</code> statements this might split.
+ * When scheduling early a store might be moved out of the loop but then there are two edges alive.
+ * The one through the store node and the adjacent one. This is an invalid schedule and instead of
+ * handling this case a late scheduler does not have this problem as memory edges are combined
+ * through phi nodes.
+ * <br>
+ * <br>
+ * A bit about this scheduler. It first discovers all alive nodes and allocates side data for them.
+ * Then the control flow graph is build. Then, all phis are placed and finally all the remaining nodes
+ * in an order where a node is placed when all alive uses are placed. Finally, the output is produced.
+ */
+public class Scheduler {
+
+    /**
+     * A basic block with a schedule of the containing nodes.
+     *
+     * @param nodes The nodes in the final schedule of this block
+     * @param exit The exit node of this block.
+     * @param exitId In case the next block is a region this gives the entry id into the region.
+     * @param next The next blocks.
+     */
+    public record Block(Node[] nodes, Node exit, int exitId, Block[] next) {}
+
+    /**
+     * Definition of a block in the building process.
+     */
+    private static class BasicBlock {
+
+        /**
+         * Dominator of this block
+         */
+        final BasicBlock dom;
+        /**
+         * Id of this block where <code>a.depth < b.depth</code> means that a is before b or
+         * both are in different branches.
+         */
+        final int depth;
+        /**
+         * Previous blocks
+         */
+        final BasicBlock[] prev;
+        /**
+         * Entry to this block
+         */
+        final Node entry;
+        /**
+         * Schedules node in reverse order.
+         */
+        final ArrayList<Node> reverseSchedule = new ArrayList<>();
+
+        /**
+         * Initialize the block.
+         * @param entry The node that started this block
+         * @param depth The depth of this node. All previous nodes need to have a lower value.
+         * @param prev The previous blocks.
+         */
+        BasicBlock(Node entry, int depth, BasicBlock... prev) {
+            BasicBlock dom = null;
+            int max = -1;
+            for(var bb: prev) {
+                max = Math.max(max, bb.depth);
+                dom = dom==null?bb:dom(dom, bb);
+            }
+            assert depth > max;
+            this.dom = dom;
+            this.depth = depth;
+            this.entry = entry;
+            this.prev = prev;
+        }
+        BasicBlock(Node entry, BasicBlock prev) {
+            this(entry,prev.depth+1,prev);
+        }
+
+    }
+
+    /**
+     * Ancillary data for nodes used during the scheduling process.
+     */
+    private static class NodeData {
+
+        /**
+         * The node this ancillary data is used for.
+         */
+        final Node node;
+
+        /**
+         * Number of alive users not yet scheduled.
+         */
+        int users = 1;
+
+        /**
+         * Block into which the node should be placed so far.
+         * This will be updated with every placed use.
+         */
+        BasicBlock block;
+
+        /**
+         * Initialize ancillary data for a node
+         * @param node The node this ancillary data is associated with.
+         */
+        NodeData(Node node) {
+            this.node = node;
+        }
+
+    }
+
+    /**
+     * Ancillary data for nodes.
+     */
+    private final IdentityHashMap<Node, NodeData> data = new IdentityHashMap<>();
+    /**
+     * List of nodes which can be placed since all users are placed.
+     */
+    private final Stack<NodeData> scheduleQueue = new Stack<>();
+
+    /**
+     * Get the ancillary data for an alive node.
+     * @param node The node for which the ancillary data is requested.
+     * @return The ancillary data for the node.
+     */
+    NodeData d(Node node) {
+        return od(node).orElseThrow(AssertionError::new);
+    }
+
+    /**
+     * Get the ancillary data for a potentially dead node.
+     * @param node The node for which the ancillary data is requested.
+     * @return The ancillary data for the node an alive node or
+     * <code>Optional.empty()</code> for <code>null</code> or dead nodes.
+     */
+    Optional<NodeData> od(Node node) {
+        return Optional.ofNullable(data.get(node));
+    }
+
+    /**
+     * Checks a node for validity
+     * @param data The node to check.
+     * @return true if all placed inputs are before this node.
+     */
+    private boolean isValid(NodeData data) {
+        return data.node._inputs.stream()
+                .map(i->i==null?null:d(i))
+                .map(d->d==null||d.users>0?null:d.block)
+                .allMatch(d->d==null||dom(d, data.block)==d);
+    }
+
+    /**
+     * Checks that node is not XCtrl.
+     * @param node The node to check.
+     * @return true if the node is not XCtrl.
+     */
+    private static boolean isNotXCtrl(Node node) {
+        return !(node instanceof ConstantNode c && c.compute() == Type.XCONTROL) && !(node instanceof XCtrlNode);
+    }
+
+    /**
+     * Return the dominator of <code>a</code> and <code>b</code>
+     * @param a Block a
+     * @param b Block b
+     * @return The dominator of <code>a</code> and <code>b</code>
+     */
+    private static BasicBlock dom(BasicBlock a, BasicBlock b) {
+        while (a!=b) {
+            if (a.depth >= b.depth) a=a.dom;
+            if (b.depth > a.depth) b=b.dom;
+        }
+        return a;
+    }
+
+    /**
+     * Return if a is before b.
+     * @param a Block a
+     * @param b Block b
+     * @return true is a is before b.
+     */
+    private static boolean isBefore(BasicBlock a, BasicBlock b) {
+        while (b.depth > a.depth) {
+            while (b.dom.depth > a.depth) b = b.dom;
+            for (int i=0; i<b.prev.length-1; i++) {
+                if (isBefore(a, b.prev[i])) return true;
+            }
+            b = b.prev[b.prev.length-1];
+        }
+        return a == b;
+    }
+
+    /**
+     * Is node placed during the control flow graph build.
+     * @param data Node to check.
+     * @return true if node is placed during the control flow graph build.
+     */
+    private static boolean isPinnedNode(NodeData data) {
+        return data.node instanceof CFGNode || data.node instanceof PhiNode;
+    }
+
+    /**
+     * Refine placement of a node.
+     * @param data The node to refine.
+     * @param block The block before the node should be scheduled.
+     */
+    private void refinePlacement(NodeData data, BasicBlock block) {
+        assert !isPinnedNode(data);
+        data.block = data.block == null ? block : dom(data.block, block);
+        assert isValid(data);
+    }
+
+    /**
+     * Refine placement if before is happening before data
+     * @param data The node for which the placement should be refined.
+     * @param before The node before which the data node should be placed.
+     */
+    private void optionalRefinePlacement(NodeData data, Node before) {
+        od(before).ifPresent(d->{
+            // before might be in a different branch. So check this case with isBefore
+            // and only refine the placement if it is not in a different branch.
+            if (isBefore(d.block, data.block)) refinePlacement(data, d.block);
+        });
+    }
+
+    /**
+     * Schedule all nodes not yet scheduled.
+     */
+    private void doSchedule() {
+        while (!scheduleQueue.isEmpty()) {
+            var data = scheduleQueue.pop();
+            assert !isPinnedNode(data);
+
+            assert data.block != null;
+            assert data.users == 0;
+
+            if (data.node instanceof LoadNode l) {
+                assert isValid(data);
+                // Handle anti-deps of load nodes.
+                // At this point all anti-dep nodes are scheduled,
+                // but they did not refine the placement
+                // so do that now.
+                var mem = l.in(1);
+                for(var out : mem._outputs) {
+                    if (out instanceof PhiNode p) {
+                        var r = p.in(0);
+                        for (int i = 1; i < p.nIns(); i++) {
+                            if (p.in(i) == mem) optionalRefinePlacement(data, r.in(i));
+                        }
+                    } else if (!(out instanceof LoadNode)) {
+                        optionalRefinePlacement(data, out);
+                    }
+                }
+            }
+
+            assert isValid(data);
+            data.block.reverseSchedule.add(data.node);
+
+            for(var in:data.node._inputs) {
+                if (in!=null) update(d(in), data.block);
+            }
+            if (data.node instanceof StoreNode s) {
+                // Store nodes have anti-deps to load nodes.
+                // So decrease the uses of these loads when the store is placed.
+                for (var out: s.in(1)._outputs) {
+                    if (out instanceof LoadNode) od(out).ifPresent(this::decUsers);
+                }
+            }
+        }
+
+        // Now all nodes should be placed and have a block assigned
+        assert this.data.values().stream().noneMatch(d->d.block==null);
+    }
+
+    /**
+     * Decrement the not-yet-placed users of a block.
+     * @param data The node for which the users should be decremented.
+     */
+    private void decUsers(NodeData data) {
+        assert data.users > 0;
+        if (--data.users == 0) {
+            assert data.block != null;
+            assert isValid(data);
+
+            // When all users are gone this node can be scheduled.
+            scheduleQueue.push(data);
+        }
+    }
+
+    /**
+     * Update the placement of a node
+     * @param data The node to update
+     * @param block The block before which the node should happen.
+     */
+    private void update(NodeData data, BasicBlock block) {
+        assert block != null;
+        if (data.users == 0) {
+            assert isPinnedNode(data);
+            return;
+        }
+        refinePlacement(data, block);
+        decUsers(data);
+    }
+
+    /**
+     * Checks if a CFG node is ready to be placed. This is used for regions joining branches.
+     * @param node The CFG node to check
+     * @return true if all parents of a CFG node are placed.
+     */
+    private boolean isCFGNodeReady(Node node) {
+        if (node instanceof LoopNode l) {
+            assert d(l.in(1)).block != null;
+        } else if (node instanceof RegionNode r) {
+            for(int i=1; i<r.nIns(); i++) {
+                if (od(r.in(i)).map(d->d.block==null).orElse(false)) return false;
+            }
+        } else if (node instanceof XCtrlNode) {
+            return false;
+        } else {
+            assert d(node.in(0)).block != null;
+        }
+        return true;
+    }
+
+    /**
+     * Schedule all phi nodes.
+     * @param phiQueue List of all the phi nodes to schedule.
+     */
+    private void schedulePhis(Stack<NodeData> phiQueue) {
+        while(!phiQueue.empty()) {
+            var data = phiQueue.pop();
+            var phi = (PhiNode) data.node;
+            var r = phi.in(0);
+            data.block = d(r).block;
+            for(int i=1; i<phi.nIns(); i++) {
+                var in = phi.in(i);
+                od(r.in(i)).ifPresent(d->update(d(in), d.block));
+            }
+        }
+    }
+
+    /**
+     * Build the control flow graph.
+     * @param start The start node.
+     */
+    private void doBuildCTF(StartNode start) {
+        var queue = new Stack<NodeData>();
+        var phiQueue = new Stack<NodeData>();
+        queue.push(d(start));
+        while (!queue.isEmpty()) {
+            var data = queue.pop();
+            var node = data.node;
+            assert node instanceof CFGNode;
+            BasicBlock block = switch (node) {
+            case StartNode s -> new BasicBlock(s, 0);
+            case LoopNode l -> new BasicBlock(l, d(l.in(1)).block);
+            case RegionNode r -> {
+                    var prev = new ArrayList<BasicBlock>();
+                    int depth = 0;
+                    for(int i=1; i<r.nIns(); i++) {
+                        if( !od(r.in(i)).isPresent() ) continue;
+                        BasicBlock bb = d(r.in(i)).block;
+                        prev.add(bb);
+                        depth = Math.max(depth,bb.depth);
+                    }
+                    yield new BasicBlock(r, depth+1, prev.toArray(BasicBlock[]::new));
+            }
+            case IfNode i -> d(i.in(0)).block;
+            case ReturnNode ret -> d(ret .in(0)).block;
+            case CallNode call -> throw Utils.TODO();
+            default -> new BasicBlock(node, d(node.in(0)).block);
+            };
+            data.block = block;
+            if (node instanceof RegionNode r) {
+                // Regions might have phis which need to be scheduled.
+                // Put them on a list for later scheduling.
+                for (var out:r._outputs) {
+                    if (out instanceof PhiNode p) {
+                        var d = this.data.get(p);
+                        if (d!=null) {
+                            d.users=0;
+                            phiQueue.push(d);
+                        }
+                    }
+                }
+            }
+            if( node instanceof FunNode fun ) {
+                // Cannot find CFG user from fun via a naive search, because always find
+                // Return but Return is not always the one CFG user.
+                CFGNode n = fun.uctrl();
+                assert isCFGNodeReady(n) && d(n).block==null;
+                queue.push(d(n));
+            } else if( !(node instanceof ReturnNode) ) {
+                for (Node n : node._outputs)
+                    if(n instanceof CFGNode && isCFGNodeReady(n) && d(n).block == null)
+                        queue.push(d(n));
+            }
+            var b = block;
+            for(var in:data.node._inputs) od(in).ifPresent(d->update(d, b));
+        }
+
+        // Schedule all phi nodes.
+        schedulePhis(phiQueue);
+    }
+
+    /**
+     * Mark a node alive and create ancillary data for it.
+     * @param queue List into which this node should be placed if it needs to be visited.
+     * @param node Node which should be marked alive.
+     * @param cfg If this node is a CFG node.
+     */
+    private void markAlive(Stack<NodeData> queue, Node node, boolean cfg) {
+        var nd = od(node).orElse(null);
+        if (nd != null) {
+            // Node was already visited, just increase the users.
+            if (nd.users>0) nd.users++;
+            return;
+        }
+        assert node instanceof CFGNode == cfg;
+        assert isNotXCtrl(node);
+        nd = new NodeData(node);
+        if (cfg) nd.users=0;
+        data.put(node, nd);
+        queue.push(nd);
+    }
+
+    /**
+     * Mark all alive nodes.
+     * First all CFG nodes are marked, then all other nodes.
+     * @param node THe start node.
+     */
+    private void doMarkAlive(Node node) {
+        var cfgQueue = new Stack<NodeData>();
+        var dataQueue = new Stack<NodeData>();
+        var mem = new Stack<NodeData>();
+        markAlive(cfgQueue, node, true);
+        // Mark all CFG nodes.
+        while (!cfgQueue.isEmpty()) {
+            var data = cfgQueue.pop();
+            node = data.node;
+            assert node instanceof CFGNode;
+            if (!(node instanceof ReturnNode) ) {
+                for (var out : node._outputs) if (out!=null && out instanceof CFGNode && isNotXCtrl(out)) markAlive(cfgQueue, out, true);
+            }
+            for (var in : node._inputs) if(in!=null && !(in instanceof CFGNode) && isNotXCtrl(in)) markAlive(dataQueue, in, false);
+        }
+        // Mark all other nodes.
+        while (!dataQueue.isEmpty()) {
+            var data = dataQueue.pop();
+            node = data.node;
+            assert !(node instanceof CFGNode);
+            if (node instanceof PhiNode phi) {
+                var r = phi.in(0);
+                for (int i=1; i<phi.nIns(); i++) {
+                    if (od(r.in(i)).isPresent()) markAlive(dataQueue, phi.in(i), false);
+                }
+            } else {
+                for (var in : node._inputs) if (in != null && !(in instanceof CFGNode)) markAlive(dataQueue, in, false);
+            }
+            if (node instanceof StoreNode) mem.push(data);
+        }
+        // Handle store nodes and increase load with an anti-dep to the store.
+        while (!mem.isEmpty()) {
+            var data = mem.pop();
+            node = data.node;
+            for(var out:node.in(1)._outputs) {
+                if (out instanceof LoadNode) od(out).ifPresent(d->d.users++);
+            }
+        }
+    }
+
+    /**
+     * Helper function to append the nodes of a block to an array of nodes
+     * @param arr The array the nodes of a block should be appended to.
+     * @param node A potentially separator node
+     * @param block The block from which the nodes should be appended.
+     * @return The combined new array.
+     */
+    private static Node[] appendNodes(Node[] arr, Node node, BasicBlock block) {
+        var idx = arr.length;
+        arr = Arrays.copyOf(arr, arr.length+block.reverseSchedule.size()+(node==null?0:1));
+        if (node != null) arr[idx++] = node;
+        for(int i=block.reverseSchedule.size()-1;i>=0;i--) {
+            arr[idx++] = block.reverseSchedule.get(i);
+        }
+        return arr;
+    }
+
+    /**
+     * Find the CFG output of a node
+     * @param node The node
+     * @return The CFG output of the node.
+     */
+    private static CFGNode findSingleCFGOut(Node node) {
+        if (node instanceof StartNode) {
+            for(var n:node._outputs)
+                if (n instanceof FunNode fun && "main".equals(fun._name) )
+                   return fun;
+            return null;
+        }
+        if( node instanceof FunNode fun ) return fun.uctrl();
+        assert node._outputs.stream().filter(x -> x instanceof CFGNode).limit(2).count()<=1;
+        for(var n:node._outputs) if(n instanceof CFGNode cfg) return cfg;
+        return null;
+    }
+
+    /**
+     * Build the final data structure after all the scheduling happened.
+     * @param start The start node
+     * @return The final schedule.
+     */
+    private Block build(Node start) {
+        var blocks = new IdentityHashMap<Node, Block>();
+        var queue = new Stack<NodeData>();
+        queue.push(d(start));
+
+        // Visit all CFG nodes and create blocks for them.
+        // This can combine blocks.
+        while(!queue.isEmpty()) {
+            var data = queue.pop();
+            var first = data.node;
+            Node prev;
+            var last = first;
+            Node[] arr = new Node[0];
+            if (first instanceof RegionNode) {
+                var nodes = new ArrayList<Node>();
+                for(var out: first._outputs) {
+                    if (out instanceof PhiNode) {
+                        if(od(out).isPresent()) nodes.add(out);
+                    }
+                }
+                arr = nodes.toArray(arr);
+            }
+            arr = appendNodes(arr, null, data.block);
+            assert !(first instanceof IfNode);
+            for(;;) {
+                prev = last;
+                last = findSingleCFGOut(last);
+                if (last == null) break;
+                if (last instanceof RegionNode) {
+                    if (blocks.get(last) == null && last != first)
+                        queue.push(d(last));
+                    break;
+                }
+                if (last instanceof ReturnNode) break;
+                if (last instanceof IfNode if_) {
+                    for(var out:if_._outputs) if (out instanceof CFGNode && blocks.get(out) == null) queue.push(d(out));
+                    break;
+                }
+                data = d(last);
+                arr = appendNodes(arr, data.node, data.block);
+            }
+            blocks.put(first, switch(last) {
+                case null -> new Block(arr, null, -1, new Block[0]);
+                case IfNode i -> new Block(arr, i, -1, new Block[2]);
+                case RegionNode r -> new Block(arr, r, r._inputs.find(prev), new Block[1]);
+                case ReturnNode r -> new Block(arr, r   , -1, new Block[0]);
+                default -> throw new AssertionError("Unexpected block exit node");
+            });
+        }
+        // Update the next pointer of all blocks.
+        for (var block: blocks.values()) {
+            switch(block.exit) {
+                case null: break;
+                case IfNode i:
+                    for(var out:i._outputs) if (out instanceof CProjNode p) block.next[p._idx] = blocks.get(p);
+                    break;
+                case RegionNode r:
+                    block.next[0] = blocks.get(r);
+                    break;
+                default:
+                    assert block.exit instanceof ReturnNode;
+            }
+        }
+        // And return the block for the start node.
+        return blocks.get(start);
+    }
+
+    /**
+     * Create a schedule for the program reachable from start.
+     * @param start The start node
+     * @return The final schedule.
+     */
+    public static Scheduler.Block schedule(StartNode start) {
+        var scheduler = new Scheduler();
+        scheduler.doMarkAlive(start);
+        scheduler.doBuildCTF(start);
+        scheduler.doSchedule();
+        return scheduler.build(start);
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Fuzzer.java b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Fuzzer.java
new file mode 100644
index 00000000..f7e0c4ad
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Fuzzer.java
@@ -0,0 +1,174 @@
+package com.seaofnodes.simple.fuzzer;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.Eval2;
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.node.Node;
+import java.util.ArrayList;
+import java.util.Objects;
+import java.util.Random;
+import java.util.function.Consumer;
+
+/**
+ * Implementation of the fuzzer.
+ * Random testcases are generated using the ScriptGenerator.
+ * This will generate a script similar to how the parser parses it but instead of parsing it will
+ * randomly choose a variation the parser would parse and generate it.
+ * These scripts are the parsed by the parser and all exceptions are caught and filtered
+ * to only show one occurrence of one problem. This includes script which generate different
+ * results when the compiled graph with and without peeps is executed.
+ * To aid debugging scripts that cause errors are then reduced by applying rules and checking
+ * that the same issue persists.
+ */
+public class Fuzzer {
+
+    private static final int EVAL_TIMEOUT = 1000;
+
+    /**
+     * List of exceptions already encountered.
+     * This is used to filter new exceptions and discard them if they are already found.
+     */
+    private final ArrayList<Throwable> exceptions = new ArrayList<>();
+
+    /**
+     * Filter and record an exception in a script.
+     * @param e The exception caused by the script
+     * @param script The script causing the exception
+     * @param reproducer Reproducer which should be used to reproduce the test case.
+     */
+    private void recordException(Throwable e, String script, Consumer<String> reproducer, long seed) {
+        for (var ex : exceptions) {
+            if (FuzzerUtils.isExceptionFromSameCause(ex, e)) return;
+        }
+        exceptions.add(e);
+        System.out.println("========== Stack ==========");
+        e.printStackTrace(System.out);
+        System.out.println("========== Seed ==========");
+        System.out.println(seed);
+        //System.out.println("========== Code ===========");
+        //System.out.println(script);
+        System.out.println("========= Reduced =========");
+        System.out.println(Reducer.reduce(script, e, reproducer));
+        System.out.println("===========================");
+        System.out.flush();
+    }
+
+    private static boolean neq(Object a, Object b) {
+        if (Objects.equals(a, b)) return false;
+        return true;
+    }
+
+    /**
+     * Check that two graphs result in the same output when supplied with a value
+     * @param e1 Evaluator for the first graph
+     * @param e2 Evaluator for the second graph
+     * @param in The input value to both graphs to test for an equal output
+     */
+    private static void checkGraphs(CodeGen code1, CodeGen code2, long in) {
+        var r1 = Eval2.eval(code1, in, EVAL_TIMEOUT);
+        var r2 = Eval2.eval(code2, in, EVAL_TIMEOUT);
+        if( r1 == null || r2 == null ) return; // Timeout test invalid
+        if( neq(r1, r2) )
+            throw new RuntimeException("Different calculations values " + r1 + " vs " + r2);
+    }
+
+    /**
+     * Run checks for script. Compile the script with peeps enabled and disabled.
+     * Check that exceptions raised in the parser by both methods are the same and only happens if the script may be invalid.
+     * If the script was successfully parsed check that both version behave the same.
+     * @param script The script to test
+     * @param valid If the script is definitely valid. If not some exceptions may be suppressed.
+     */
+    private static void runCheck(String script, boolean valid) {
+        CodeGen code1;
+        try {
+            code1 = FuzzerUtils.parse(script, 123);
+        } catch (RuntimeException e1) {
+            try {
+                FuzzerUtils.parse(script, 456);
+            } catch (RuntimeException e2) {
+                if (FuzzerUtils.isExceptionFromSameCause(e1, e2)) {
+                    if (!valid || e1.getClass() == Parser.ParseException.class) return;
+                } else {
+                    e1.addSuppressed(e2);
+                }
+            }
+            throw e1;
+        }
+        CodeGen code2 = FuzzerUtils.parse(script, 456);
+        checkGraphs(code1, code2, 0);
+        checkGraphs(code1, code2, 1);
+        checkGraphs(code1, code2, 10);
+    }
+
+    /**
+     * Check that the script does not result in exceptions.
+     * @param script The script to test.
+     * @param valid If the script is valid or if it might contain syntax errors.
+     */
+    private void check(String script, boolean valid, long seed) {
+        try {
+            runCheck(script, valid);
+        } catch (Throwable e) {
+            recordException(e, script, s->runCheck(s, valid), seed);
+        }
+    }
+
+    /**
+     * Run one test with the given seed, and check for peephole counts.
+     * @param seed The seed to use for generating this test case
+     */
+    public int fuzzPeepTiming(long seed, int max_nids) {
+        var rand = new Random(seed);
+        var sb = new StringBuilder();
+        new ScriptGenerator(rand, sb, true).genProgram();
+        try {
+            var code = new CodeGen(sb.toString());
+
+            code.parse();
+            int nids = code.UID();
+            if( nids <= max_nids ) return max_nids; // Smaller, looking for trends as we grow
+            int parse_peeps= code._iter_cnt;
+            int parse_nops = code._iter_nop_cnt;
+            double parse_nop_ratio = (double)parse_nops/parse_peeps;
+            double parse_peeps_per_node = (double)parse_peeps/nids;
+
+            code.opto();
+            int iter_peeps= code._iter_cnt;
+            int iter_nops = code._iter_nop_cnt;
+            double iter_nop_ratio = (double)iter_nops/iter_peeps;
+            double iter_peeps_per_node = (double)iter_peeps/nids;
+
+            System.out.printf("%6d | Parsing: peeps: %5d, nops: %5d, ratio: %5.3f, last UID: %5d ps/node: %5.3f  | Iter: peeps: %6d, nops: %6d, ratio: %5.3f, ps/node: %5.3f\n",
+                              seed,
+                              parse_peeps,parse_nops,parse_nop_ratio,nids,parse_peeps_per_node,
+                              iter_peeps , iter_nops, iter_nop_ratio,      iter_peeps_per_node);
+            return nids;
+        } catch (Throwable e) {
+            // ignore exceptions, let the normal fullPeeps catch and reduce,
+            // we're interested in valid program optimizations
+        }
+        return max_nids;
+    }
+
+
+    /**
+     * Run one test with the given seed.
+     * @param seed The seed to use for generating this test case
+     */
+    public void fuzzPeeps(long seed) {
+        var rand = new Random(seed);
+        var sb = new StringBuilder();
+        var valid = new ScriptGenerator(rand, sb, true).genProgram();
+        check(sb.toString(), valid, seed);
+    }
+
+
+    /**
+     * Check that no exceptions happened.
+     * @return true if no exception happened
+     */
+    public boolean noExceptions() {
+        return exceptions.isEmpty();
+    }
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/FuzzerUtils.java b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/FuzzerUtils.java
new file mode 100644
index 00000000..0781ad67
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/FuzzerUtils.java
@@ -0,0 +1,111 @@
+package com.seaofnodes.simple.fuzzer;
+
+import com.seaofnodes.simple.CodeGen;
+import com.seaofnodes.simple.IterPeeps;
+import com.seaofnodes.simple.node.Node;
+import com.seaofnodes.simple.node.StopNode;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.io.OutputStream;
+import java.io.PrintStream;
+import java.lang.invoke.MethodHandle;
+import java.lang.invoke.MethodHandles;
+import java.lang.reflect.Field;
+import java.util.BitSet;
+
+/**
+ * Some utilities for the fuzzer.
+ */
+class FuzzerUtils {
+
+    /**
+     * Get the val of a private field
+     */
+    @SuppressWarnings("unchecked")
+    public static <T> T getFieldValue(Object obj, String name) throws NoSuchFieldException, IllegalAccessException {
+        return (T) (obj instanceof Class<?> clz ? getField(clz, name).get(null) : getField(obj.getClass(), name).get(obj));
+    }
+
+    /**
+     * Get access to a private field
+     */
+    public static Field getField(Class<?> clz, String name) throws NoSuchFieldException {
+        var field = clz.getDeclaredField(name);
+        try {
+            field.setAccessible(true);
+        } catch (Throwable e) {
+            // Intentionally left empty
+        }
+        return field;
+    }
+
+    /**
+     * Try to rethrow an exception or create a runtime exception and throw it.
+     */
+    public static RuntimeException rethrow(Throwable e) {
+        if (e instanceof RuntimeException re) return re;
+        if (e instanceof Error er) throw er;
+        return new RuntimeException(e);
+    }
+
+    /**
+     * Some problems might trigger debug output. Suppress this output with a null print stream during fuzzing.
+     */
+    public static final PrintStream NULL_PRINT_STREAM = new PrintStream(OutputStream.nullOutputStream());
+
+    /**
+     * Check that the messages are similar.
+     */
+    private static boolean similarMessages(String a, String b) {
+        if (a == null || b == null) return true;
+        a = a.replaceAll("'\\w+'", "'normalized'").replaceAll("variable \\w+", "variable normalized");
+        b = b.replaceAll("'\\w+'", "'normalized'").replaceAll("variable \\w+", "variable normalized");
+        return a.equals(b);
+    }
+
+    /**
+     * Check if both stack traces have the same first entry. Empty stack traces can happen with NPE optimization
+     * and allow the other to be any stack trace.
+     */
+    private static boolean sameStackTraceOrigin(StackTraceElement[] a, StackTraceElement[] b) {
+        if (a == null || a.length == 0 || b == null || b.length == 0) return true; // One or both stack traces are missing.
+        return a[0].equals(b[0]);
+    }
+
+    /**
+     * Checks if two exceptions are caused by the same problem.
+     */
+    public static boolean isExceptionFromSameCause(Throwable a, Throwable b) {
+        if (a == null || b == null) return a == b; // Handle the null case
+        if (a.getClass() != b.getClass()) return false; // Different classes
+        if (!similarMessages(a.getMessage(), b.getMessage())) return false; // Different messages. Null is allowed as wildcard
+        var s1 = a.getStackTrace();
+        var s2 = b.getStackTrace();
+        if (!sameStackTraceOrigin(s1, s2)) return false; // Different stack trace origins
+        if (!isExceptionFromSameCause(a.getCause(), b.getCause())) return false; // Different causes
+        var o1 = a.getSuppressed();
+        var o2 = b.getSuppressed();
+        if (o1 == null || o2 == null || o1.length != o2.length) return o1 == o2; // Different suppression
+        for (int i=0; i<o1.length; i++) {
+            if (!isExceptionFromSameCause(o1[i], o2[i])) return false; // Different suppression
+        }
+        return true;
+    }
+
+    /**
+     * Parse script with peepholes enabled or disabled
+     */
+    public static CodeGen parse(String script, long workListSeed) {
+        var err = System.err;
+        var out = System.out;
+        try {
+            System.setErr(NULL_PRINT_STREAM);
+            System.setOut(NULL_PRINT_STREAM);
+            var code = new CodeGen(script, TypeInteger.BOT, workListSeed);
+            return code.parse().opto().typeCheck().GCM().localSched();
+        } finally {
+            System.setErr(err);
+            System.setOut(out);
+        }
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Reducer.java b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Reducer.java
new file mode 100644
index 00000000..3731b40c
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/Reducer.java
@@ -0,0 +1,176 @@
+package com.seaofnodes.simple.fuzzer;
+
+import java.util.Arrays;
+import java.util.function.BiConsumer;
+import java.util.function.Consumer;
+import java.util.function.Predicate;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ * This class is used to reduce test cases created by the fuzzer.
+ * It applies rewrite rules to the test case and checks that the
+ * test still produces the same exception.
+ * This is done in a fixpoint iteration until every rewrite produces
+ * no or a different exception.
+ */
+public class Reducer {
+
+    private interface Replacer extends BiConsumer<StringBuilder, Matcher> {}
+
+    /**
+     * Holder for the rewrite rules
+     */
+    private record Replace(Pattern pattern, boolean iterate, Replacer... replacements) {
+        Replace(Pattern p, Object... replacements) {
+            this(p, replacements[0] == Boolean.TRUE, Arrays.stream(replacements).filter(o->!(o instanceof Boolean)).map(Replace::from).toArray(Replacer[]::new));
+        }
+        private static Replacer from(Object o) {
+            if (o instanceof Replacer r) return r;
+            if (o instanceof Integer i) return (s, m)->s.append(m.group(i));
+            if (o instanceof String r) return (s, m)->s.append(r);
+            throw new IllegalArgumentException();
+        }
+    }
+
+    /**
+     * List of rewrite rules.
+     */
+    private static final Replace[] REPLACEMENTS = {
+            new Replace(Pattern.compile("\\b(?:[^\\W0]|\\w\\w+)\\b"), "0", "1"),
+            new Replace(Pattern.compile("(?<=\\n|^)[^\\n]+(?=\\n|$)"), true, ""),
+            new Replace(Pattern.compile("(?<=[+\\-*/<>=(])--"), ""),
+            new Replace(Pattern.compile("\\b--"), "+"),
+            new Replace(Pattern.compile("-"), ""),
+            new Replace(Pattern.compile("\\b\\+-"), "-"),
+            new Replace(Pattern.compile("(?<![+\\-*/<>=])(?:-|\\*|/|>=|<=|>|<|!=|==)(?![+\\-*/<>=])"), "+"),
+            new Replace(Pattern.compile("\\{((?:[^{}]|\\{})+)(?:\\n[ \\t]*)?}"), "", "{}", 1),
+            new Replace(Pattern.compile("(?<=\\n|^)([ \\t]*)\\{\\n(.*?)\\n\\1}", Pattern.DOTALL), 2),
+            new Replace(Pattern.compile("\\(([^()]+)\\)"), 1),
+            new Replace(Pattern.compile("\\d+\\+"), ""),
+            new Replace(Pattern.compile("\\+\\d+"), ""),
+            new Replace(Pattern.compile("\\n\\n+"), "\n"),
+            new Replace(Pattern.compile("^\\n+|\\n+$"), ""),
+            new Replace(Pattern.compile("else *"), ""),
+            new Replace(Pattern.compile("\\bif\\([^()]+\\) *"), ""),
+            new Replace(Pattern.compile("\\bwhile\\([^()]+\\) *"), ""),
+            new Replace(Pattern.compile("\\bstruct \\w+ \\{[^{}]*}"), "")
+    };
+
+    /**
+     * Predicate to test if the reduced script generates the same error.
+     */
+    private final Predicate<String> tester;
+
+    /**
+     * Create a reducer with a test function.
+     * @param tester Test function which returns true when the same issue is found in the script.
+     */
+    private Reducer(Predicate<String> tester) {
+        this.tester = tester;
+    }
+
+    /**
+     * Rewrites the script with one rewrite rule.
+     */
+    private String doReplacement(String script, Pattern pattern, Replacer[] replacements) {
+        var matcher = pattern.matcher(script);
+        var sb = new StringBuilder();
+        var last = 0;
+        var skip = 0;
+        outer:
+        while (matcher.find(last + skip)) {
+            sb.append(script, last, matcher.start());
+            last = matcher.end();
+            skip = last == matcher.start() ? 1 : 0;
+            var pos = sb.length();
+            for (var replacement : replacements) {
+                replacement.accept(sb, matcher);
+                var tail = sb.length();
+                sb.append(script, last, script.length());
+                if (tester.test(sb.toString())) {
+                    sb.setLength(tail);
+                    continue outer;
+                }
+                sb.setLength(pos);
+            }
+            last = matcher.start();
+            skip = 1;
+        }
+        sb.append(script, last, script.length());
+        return sb.toString();
+    }
+
+    /**
+     * Clean up variable names from the random ones generated by the fuzzer.
+     */
+    private String cleanVariables(String script) {
+        var matcher = Pattern.compile("\\b([0-9a-zA-Z_]+) ([0-9a-zA-Z_]+)").matcher(script);
+        int[] num = {0, 0};
+        while (matcher.find()) {
+            var type = matcher.group(1);
+            var var = matcher.group(2);
+            if (type.equals("new")) continue;
+            String prefix = "v";
+            int t = 0;
+            if (type.equals("struct")) {
+                t = 1;
+                prefix = "s";
+            }
+            if (var.matches(prefix+"\\d+")) continue;
+            while (script.contains(prefix+num[t])) num[t]++;
+            var n = script.replaceAll("\\b"+var+"\\b", prefix + num[t]);
+            if (tester.test(n)) {
+                script = n;
+            }
+        }
+        return script;
+    }
+
+    /**
+     * Run all rewrite rules once.
+     */
+    private String doAllReplacements(String script) {
+        for (var replace: REPLACEMENTS) {
+            String old;
+            do {
+                old = script;
+                script = doReplacement(script, replace.pattern, replace.replacements);
+            } while (replace.iterate && !old.equals(script));
+        }
+        return script;
+    }
+
+    /**
+     * Reduce the script to a minimal version which produces the same problem with a test function.
+     * @param tester Test function which returns true when the same issue is found in the script.
+     */
+    public static String reduce(String script, Predicate<String> tester) {
+        var reducer = new Reducer(tester);
+        String old;
+        do {
+            old = script;
+            script = reducer.doAllReplacements(script);
+            script = reducer.cleanVariables(script);
+        } while (!script.equals(old));
+        return script;
+    }
+
+    /**
+     * Reduce the script to a minimal version which produces the same problem with a reproducer.
+     * @param ex The exception originally caused by the script
+     * @param reproducer Test function which throws an exception which will be checked against ex.
+     */
+    public static String reduce(String script, Throwable ex, Consumer<String> reproducer) {
+        return reduce(script, s->{
+            Throwable nex = null;
+            try {
+                reproducer.accept(s);
+            } catch (Throwable e) {
+                nex = e;
+            }
+            return FuzzerUtils.isExceptionFromSameCause(nex, ex);
+        });
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
new file mode 100644
index 00000000..f119fa1a
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/fuzzer/ScriptGenerator.java
@@ -0,0 +1,869 @@
+package com.seaofnodes.simple.fuzzer;
+
+import com.seaofnodes.simple.Parser;
+import com.seaofnodes.simple.node.ScopeNode;
+import com.seaofnodes.simple.type.TypeInteger;
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Random;
+import java.util.function.Predicate;
+import static com.seaofnodes.simple.Parser.KEYWORDS;
+
+
+/**
+ * Generate a pseudo random script.
+ * This generator will generate the same script for two random number generators initialized with the same seed.
+ * To generate valid code it implements the parser but instead of parsing it emits the statements and expressions.
+ * It is guaranteed to terminate.
+ */
+public class ScriptGenerator {
+
+    private static final int MAX_STATEMENTS_PER_BLOCK = 5;
+    private static final int MAX_BINARY_EXPRESSIONS_PER_EXPRESSION = 10;
+    private static final int MAX_UNARY_EXPRESSIONS_PER_EXPRESSION = 6;
+    private static final int MAX_NAME_LENGTH = 10;
+    private static final int MAX_BLOCK_DEPTH = 4;
+    private static final int MAX_EXPRESSION_DEPTH = 10;
+    private static final int MAX_SUFFIX_RECURSIVE_DEPTH = 10;
+
+    /**
+     * Number of spaces per indentation
+     */
+    private static final int INDENTATION = 4;
+    /**
+     * Valid characters for identifiers. The last 10 are not valid for the first character.
+     */
+    private static final String VAR_CHARS = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ_0123456789";
+
+    /**
+     * Flag for a statement that it does not pass on control flow to the next statement.
+     */
+    private static final int FLAG_STOP = 0x01;
+    /**
+     * Flag for a statement that it contains a final if statement without an else branch.
+     */
+    private static final int FLAG_IF_WITHOUT_ELSE = 0x02;
+    /**
+     * Binary operators.
+     */
+    private static final String[] BINARY_OP = {"==", "!=", "<", "<=", ">", ">=", "+", "-", "*", "/", "&", ">>", ">>>", "<<"};
+    /**
+     * Unary operators.
+     */
+    private static final String[] UNARY_OP = {"-"};
+
+    private static class Type {
+        final String name;
+        Type(String name) {this.name=name;}
+        boolean isa(Type other) { return this == other; }
+    }
+
+    private static class TypeStruct extends Type {
+        record Field (String name, Type type, TypeStruct struct) {}
+        Field[] fields;
+        final TypeNullable nullable = new TypeNullable(this);
+        TypeStruct(String name) {
+            super(name);
+        }
+        boolean isa(Type other) { return this == other || other == nullable; }
+    }
+
+    private static class TypeNullable extends Type {
+
+        final Type base;
+
+        TypeNullable(Type base) {
+            super(base.name+"?");
+            this.base = base;
+        }
+
+    }
+
+    private static final Type TYPE_FLT = new Type("flt");
+
+    private static class TypeInt extends Type {
+
+        TypeInt(String name) {
+            super(name);
+        }
+
+        @Override
+        boolean isa(Type other) {
+            return super.isa(other) || other == TYPE_FLT || other instanceof TypeInt;
+        }
+    }
+
+    private static final List<TypeInt> INTTYPES = new ArrayList<>();
+
+    static {
+        for( var e : Parser.defaultTypes().entrySet() ) {
+            if( e.getValue() instanceof TypeInteger ) {
+                INTTYPES.add(new TypeInt(e.getKey()));
+            }
+        }
+    }
+
+    private static final Type TYPE_INT = INTTYPES.stream().filter(t->t.name.equals("int")).findAny().get();
+    private static final Type TYPE_BOOL = INTTYPES.stream().filter(t->t.name.equals("bool")).findAny().get();
+
+    private static class Variable {
+        final String name;
+        final Type declared;
+        final Variable shadowing;
+        Type type;
+        boolean shadowed = false;
+
+        Variable(String name, Type type, Variable var) {
+            this.name = name;
+            this.declared = type;
+            this.type = type;
+            this.shadowing = var;
+        }
+    }
+
+    /**
+     * The random number generator used for random decisions.
+     */
+    private final Random random;
+    /**
+     * Indentation depth.
+     */
+    private int indentation = 0;
+    /**
+     * Output string builder
+     */
+    private final StringBuilder sb;
+    /**
+     * Number of nested loops
+     */
+    private int loopDepth = 0;
+    /**
+     * Current scope start in the variables list.
+     */
+    private int currScopeStart = 0;
+    /**
+     * The depth of blocks allowed.
+     */
+    private int depth = MAX_BLOCK_DEPTH;
+    /**
+     * The depth of expressions allowed.
+     */
+    private int exprDepth = MAX_EXPRESSION_DEPTH;
+    /**
+     * Current variables in scope.
+     */
+    private final ArrayList<Variable> variables = new ArrayList<>();
+    /**
+     * All defined structs.
+     */
+    private final ArrayList<TypeStruct> structs = new ArrayList<>();
+    /**
+     * All forward declared structs
+     */
+    private final ArrayList<TypeStruct> forwardStructs = new ArrayList<>();
+    /**
+     * Allow to declare structs.
+     */
+    private boolean allowStructs = true;
+    /**
+     * If this needs to generate valid scripts or is also allowed to generate invalid ones.
+     */
+    private boolean generateValid;
+    /**
+     * If this script might be invalid.
+     */
+    private boolean maybeInvalid = false;
+
+
+    /**
+     *
+     * @param random the random number generator.
+     * @param sb the script will be written to this string builder.
+     * @param generateValid if the script should be guaranteed valid or if it is allowed to contain bugs.
+     */
+    public ScriptGenerator(Random random, StringBuilder sb, boolean generateValid) {
+        this.random = random;
+        this.sb = sb;
+        this.generateValid = generateValid;
+    }
+
+    /**
+     * Random number with log distribution
+     * @param max The maximum value
+     * @return A random number in the range [0, max) with higher numbers being more uncommon.
+     */
+    private int randLog(int max) {
+        max--;
+        int n = 1<<max;
+        var num = random.nextInt(n);
+        for (int i=max-1; i>=0; i--) {
+            if ((num & (1<<i))!=0) return max-i-1;
+        }
+        return max;
+    }
+
+    /**
+     * Helper function to print indentation.
+     * @return sb for chaining
+     */
+    private StringBuilder printIndentation() {
+        return sb.repeat(' ', indentation);
+    }
+
+    /**
+     * Generate a random name for variables. This might be invalid when it is a keyword.
+     * @return The random name generated
+     */
+    private StringBuilder getRandomName() {
+        int len = random.nextInt(MAX_NAME_LENGTH) + 1;
+        StringBuilder sb = new StringBuilder(len);
+        sb.append(VAR_CHARS.charAt(random.nextInt(VAR_CHARS.length()-10)));
+        for (int i=1; i<len; i++)
+            sb.append(VAR_CHARS.charAt(random.nextInt(VAR_CHARS.length())));
+        return sb;
+    }
+
+    /**
+     * Should invalid code be generated?
+     * @return True if invalid code should be generated
+     */
+    private boolean generateInvalid() {
+        if (generateValid || random.nextInt(1000)>2) return false;
+        maybeInvalid = true;
+        return true;
+    }
+
+    /**
+     * Lookup a variable by name
+     * @param name name of the variable
+     * @return The index of the variable in variables or -1
+     */
+    private int lookup(String name) {
+        for (int i=variables.size()-1; i>=0; i--) {
+            if (variables.get(i).name.equals(name)) return i;
+        }
+        return -1;
+    }
+
+    /**
+     * Lookup a variable by name
+     * @param name name of the variable
+     * @return THe variable of null if not found
+     */
+    private Variable lookupVar(String name) {
+        int idx = lookup(name);
+        return idx == -1 ? null : variables.get(idx);
+    }
+
+    /**
+     * Add a variable to the current scope
+     * @param name The name of the variable
+     * @param type The declared type of the variable
+     */
+    private void addVariable(String name, Type type) {
+        var old = lookupVar(name);
+        variables.add(new Variable(name, type, old));
+        if (old != null) old.shadowed = true;
+    }
+
+    /**
+     * Pop variables to level to
+     * @param to Level until which variables should be popped
+     */
+    private void popVariables(int to) {
+        while (variables.size() > to) {
+            var v = variables.removeLast();
+            if (v.shadowing != null) v.shadowing.shadowed = false;
+        }
+    }
+
+    /**
+     * Get a random visible variable patching pred
+     * @param pred The predicate the variable needs to match
+     * @return A random visible variable matching pred or null if no variable mached pred.
+     */
+    private Variable findVisibleVariablesMatching(Predicate<Variable> pred) {
+        int num=0;
+        for (var v:variables) {
+            if (!v.shadowed && pred.test(v)) num++;
+        }
+        if (num == 0) return null;
+        num = random.nextInt(num);
+        for (var v:variables) {
+            if (!v.shadowed && pred.test(v) && num-- == 0) return v;
+        }
+        throw new AssertionError();
+    }
+
+    /**
+     * Get a structure by name
+     * @param name Name of the structure
+     * @return The structure of null
+     */
+    private TypeStruct getStruct(String name) {
+        for (var s:structs) {
+            if (s.name.equals(name)) return s;
+        }
+        for (var s:forwardStructs) if (s.name.equals(name)) return s;
+        return null;
+    }
+
+    /**
+     * Generate a variable name. This might be new random name or a name from an outer scope.
+     * If the program is allowed to be invalid this can return keywords and already used variable names in the current scope.
+     * @return The variable name.
+     */
+    private String getVarName() {
+        if (currScopeStart > 0 && random.nextInt(10) > 7) {
+            // Use a variable outside the current scope.
+            var v = variables.get(random.nextInt(currScopeStart));
+            if (lookup(v.name) < currScopeStart) return v.name;
+            if (!generateValid) {
+                maybeInvalid = true;
+                return v.name;
+            }
+        }
+        // Generate a new random variable name
+        StringBuilder sb = getRandomName();
+        var v = sb.toString();
+        if (!generateValid && (KEYWORDS.contains(v) || lookup(v) >= currScopeStart)) {
+            maybeInvalid = true;
+            return v;
+        }
+        while (KEYWORDS.contains(v) || lookup(v) >= currScopeStart) {
+            sb.append(VAR_CHARS.charAt(random.nextInt(VAR_CHARS.length())));
+            v = sb.toString();
+        }
+        return v;
+    }
+
+    private <T> T randFromList(List<T> list) {
+        return list.get(random.nextInt(list.size()));
+    }
+
+    /**
+     * Get a random structure name
+     * @return A random structure name
+     */
+    private String getStructName() {
+        if (!structs.isEmpty() && generateInvalid()) return randFromList(structs).name;
+        if (!forwardStructs.isEmpty() && generateInvalid()) return randFromList(forwardStructs).name;
+
+        // Generate a new random struct name
+        StringBuilder sb = getRandomName();
+        var v = sb.toString();
+        if (!generateValid && (KEYWORDS.contains(v) || getStruct(v) != null)) {
+            maybeInvalid = true;
+            return v;
+        }
+        while (KEYWORDS.contains(v) || getStruct(v) != null) {
+            sb.append(VAR_CHARS.charAt(random.nextInt(VAR_CHARS.length())));
+            v = sb.toString();
+        }
+        return v;
+    }
+
+    public TypeInt getIntType() {
+        return randFromList(INTTYPES);
+    }
+
+    /**
+     * Get a random type
+     * @return A random type
+     */
+    private Type getType(boolean allowForward) {
+        int t = random.nextInt(10);
+        if( t<5 || structs.isEmpty() ) return getIntType();
+        if( t<7 ) return TYPE_FLT;
+        if (allowForward && random.nextInt(10)==0) {
+            int i=random.nextInt(forwardStructs.size()+1);
+            if (i>0) return forwardStructs.get(i-1).nullable;
+            var name = getStructName();
+            var struct = new TypeStruct(name);
+            forwardStructs.add(struct);
+            return struct.nullable;
+        }
+        TypeStruct struct = randFromList(structs);
+        if (random.nextBoolean()) return struct.nullable;
+        return struct;
+    }
+
+    private Type getType() {
+        return getType(false);
+    }
+
+    /**
+     * Generates a program and writes it into the string builder supplied in the constructor.
+     * @return If the program is allowed to be invalid returns if something potentially invalid was generated.
+     */
+    public boolean genProgram() {
+        var oldGenerateValid = generateValid;
+        if (!generateValid && random.nextBoolean()) generateValid = true;
+        this.maybeInvalid = false;
+        addVariable(ScopeNode.ARG0, TYPE_INT);
+        currScopeStart = variables.size();
+        if ((genStatements() & FLAG_STOP) == 0) {
+            if (generateValid || random.nextInt(10)<7) {
+                genReturn();
+            } else {
+                this.maybeInvalid = true;
+            }
+        }
+        generateValid = oldGenerateValid;
+        return !this.maybeInvalid;
+    }
+
+    /**
+     * Generate a list of statements.
+     * @return flags FLAG_STOP and FLAG_IF_WITHOUT_ELSE for the last statement generated
+     */
+    public int genStatements() {
+        var num = random.nextInt(MAX_STATEMENTS_PER_BLOCK * (depth+1));
+        for (int i=0; i<num; i++) {
+            printIndentation();
+            var stop = genStatement();
+            sb.append("\n");
+            if ((stop & FLAG_STOP) != 0) return stop;
+        }
+        return 0;
+    }
+
+    /**
+     * Generate a single statement
+     * @return flags FLAG_STOP and FLAG_IF_WITHOUT_ELSE for the generated statement
+     */
+    public int genStatement() {
+        return switch (random.nextInt(12)) {
+            case 0 -> allowStructs || generateInvalid() ? genStruct() : genAssignment();
+            case 1 -> genBlock();
+            case 2 -> genIf();
+            case 3 -> genCountedLoop();
+            case 4 -> genWhile();
+            case 5, 6 -> genDecl();
+            case 7, 8, 9 -> genAssignment();
+            case 10 -> genNullCheck();
+            default -> genExit();
+        };
+    }
+
+    /**
+     * Generate a new structure
+     * @return 0
+     */
+    public int genStruct() {
+        int idx = random.nextInt(forwardStructs.size()+10);
+        TypeStruct struct;
+        if (idx < 10) {
+        var name = getStructName();
+            struct = new TypeStruct(name);
+            forwardStructs.add(struct);
+        } else {
+            struct = forwardStructs.get(idx-10);
+        }
+        var fields = new TypeStruct.Field[generateInvalid() ? 0 : random.nextInt(10)];
+        sb.append("struct ").append(struct.name).append(" {\n");
+        indentation += INDENTATION;
+        for (int i=0; i<fields.length; i++) {
+            var fieldName = getRandomName();
+            var type = getType(true);
+            printIndentation().append(type.name).append(" ").append(fieldName).append(";\n");
+            fields[i] = new TypeStruct.Field(fieldName.toString(), type, struct);
+        }
+        indentation -= INDENTATION;
+        printIndentation().append("};");
+        struct.fields = fields;
+        forwardStructs.remove(struct);
+        structs.add(struct);
+        return 0;
+    }
+
+    /**
+     * Generate a statement for if, else and while blocks.
+     * This is special since it disallows declarations and prefers to generate blocks.
+     * @return flags FLAG_STOP and FLAG_IF_WITHOUT_ELSE for the generated statement
+     */
+    public int genStatementBlock() {
+        var oldAllowStructs = allowStructs;
+        allowStructs = false;
+        indentation += INDENTATION;
+        int res;
+        if (depth == 0) {
+            res = random.nextBoolean() ? genAssignment() : genExit();
+        } else {
+            depth--;
+            res = switch (random.nextInt(12)) {
+                case 1, 2, 3, 4, 5 -> {
+                    depth++;
+                    indentation -= INDENTATION;
+                    var ret = genBlock();
+                    indentation += INDENTATION;
+                    depth--;
+                    yield ret;
+                }
+                case 6 -> genIf();
+                case 7 -> genCountedLoop();
+                case 8 -> genWhile();
+                case 9 -> genAssignment();
+                case 10 -> genNullCheck();
+                default -> genExit();
+            };
+            depth++;
+        }
+        indentation -= INDENTATION;
+        allowStructs = oldAllowStructs;
+        return res;
+    }
+
+    /**
+     * Generate an exit. This can be return or break and continue when in a loop.
+     * @return FLAG_STOP
+     */
+    public int genExit() {
+        if (loopDepth == 0 && generateValid) return genReturn();
+        return switch (random.nextInt(7)) {
+            case 0,1,2 -> {
+                if (loopDepth == 0) maybeInvalid = true;
+                sb.append("continue;");
+                yield FLAG_STOP;
+            }
+            case 3,4,5 -> {
+                if (loopDepth == 0) maybeInvalid = true;
+                sb.append("break;");
+                yield FLAG_STOP;
+            }
+            default -> genReturn();
+        };
+    }
+
+    /**
+     * Generate a block statement. After a certain depth only empty blocks are generated to ensure termination of the generator.
+     * @return flag FLAG_STOP for the generated statement
+     */
+    public int genBlock() {
+        if (depth == 0) {
+            sb.append("{}");
+            return 0;
+        }
+        var oldAllowStructs = allowStructs;
+        var oldCSS = currScopeStart;
+        allowStructs = false;
+        currScopeStart = variables.size();
+        depth--;
+        sb.append("{\n");
+        indentation += INDENTATION;
+        var stop = genStatements();
+        indentation -= INDENTATION;
+        printIndentation().append("}");
+        popVariables(currScopeStart);
+        depth++;
+        currScopeStart = oldCSS;
+        allowStructs = oldAllowStructs;
+        return stop & ~FLAG_IF_WITHOUT_ELSE;
+    }
+
+    /**
+     * Generate an if statement with an optional else block.
+     * @return flags FLAG_STOP and FLAG_IF_WITHOUT_ELSE for the generated statement
+     */
+    public int genIf() {
+        sb.append("if(");
+        genExpression(TYPE_BOOL, true);
+        sb.append(") ");
+        var stop = genStatementBlock();
+        if ((stop & FLAG_IF_WITHOUT_ELSE) == 0 && random.nextInt(10) > 3) {
+            sb.append("\n");
+            printIndentation().append("else ");
+            stop &= genStatementBlock();
+        } else {
+            stop = FLAG_IF_WITHOUT_ELSE;
+        }
+        return stop;
+    }
+
+    /**
+     * Generate a block with a null check
+     * if (nullable) { handle_nullable_as_non_nullable; }
+     */
+    public int genNullCheck() {
+        var v = findVisibleVariablesMatching(va->va.declared instanceof TypeNullable);
+        if (v == null) return genIf();
+        var n = (TypeNullable)v.declared;
+        boolean negate = random.nextBoolean();
+        sb.append("if(");
+        if (negate) sb.append("!");
+        sb.append(v.name).append(")");
+        if (!negate) v.type = n.base;
+        var stop = genStatementBlock();
+        v.type = n;
+        if ((stop & FLAG_IF_WITHOUT_ELSE) == 0 && random.nextInt(10) > 3) {
+            sb.append("\n");
+            printIndentation().append("else ");
+            if (negate) v.type = n.base;
+            stop &= genStatementBlock();
+            v.type = n;
+        } else {
+            stop = FLAG_IF_WITHOUT_ELSE;
+        }
+        return stop;
+    }
+
+    /**
+     * Generate a while loop.
+     * @return 0
+     */
+    public int genWhile() {
+        sb.append("while(");
+        genExpression(TYPE_BOOL, true);
+        sb.append(") ");
+        loopDepth++;
+        genStatementBlock();
+        loopDepth--;
+        return 0;
+    }
+
+    /**
+     * Generate a counted loop of the form
+     * <code>
+     *     {
+     *         int varname = start_expr;
+     *         while (varname < end_expr) loop_body;
+     *     }
+     * </code>
+     * @return 0
+     */
+    public int genCountedLoop() {
+        if (depth == 0) return genWhile();
+        var oldCSS = currScopeStart;
+        currScopeStart = variables.size();
+        sb.append("{\n");
+        indentation += INDENTATION;
+        String name = getVarName();
+        printIndentation().append("int ").append(name).append("=");
+        genExpression(TYPE_INT, true);
+        sb.append(";\n");
+        addVariable(name, TYPE_INT);
+        printIndentation().append("while(").append(name).append("<");
+        genExpression(TYPE_INT, true);
+        sb.append(") {\n");
+        indentation += INDENTATION;
+        depth--;
+        loopDepth++;
+        printIndentation().append(name).append("=").append(name).append("+");
+        genExpression(TYPE_INT, true);
+        sb.append(";\n");
+        genStatements();
+        loopDepth--;
+        depth++;
+        indentation -= INDENTATION;
+        printIndentation().append("}\n");
+        indentation -= INDENTATION;
+        printIndentation().append("}");
+        popVariables(currScopeStart);
+        currScopeStart = oldCSS;
+        return 0;
+    }
+
+    /**
+     * Generate a declaration statement.
+     * @return 0
+     */
+    public int genDecl() {
+        var type = getType();
+        var name = getVarName();
+        // Always make them mutable
+        sb.append(generateInvalid() ? getRandomName() : type.name).append(" !").append(name);
+        if (!(type instanceof TypeNullable) || random.nextBoolean()) {
+            sb.append("=");
+            genExpression(type, true);
+        }
+        sb.append(";");
+        addVariable(name, type);
+        return 0;
+    }
+
+    /**
+     * Generate an assignment statement.
+     * @return 0
+     */
+    public int genAssignment() {
+        Type type;
+        Type declared;
+        if (generateInvalid()) {
+            sb.append(getRandomName());
+            type = getType();
+            declared = type;
+        } else {
+            var v = findVisibleVariablesMatching(va->true);
+            if (v == null) return genDecl();
+            sb.append(v.name);
+            type = v.type;
+            declared = v.declared;
+        }
+        if (generateInvalid()) {
+            var name = getRandomName();
+            sb.append(".").append(name);
+            declared = getType();
+        } else if (type instanceof TypeStruct s && s.fields.length > 0 && random.nextBoolean()) {
+            var field = s.fields[random.nextInt(s.fields.length)];
+            sb.append(".").append(field.name);
+            declared = field.type;
+        }
+        sb.append("=");
+        genExpression(declared, true);
+        sb.append(";");
+        return 0;
+    }
+
+    /**
+     * Generate a return statement.
+     * @return FLAG_STOP
+     */
+    public int genReturn() {
+        var type = getType();
+        sb.append("return ");
+        genExpression(type, true);
+        sb.append(";");
+        return FLAG_STOP;
+    }
+
+    /**
+     * Generate a binary expression.
+     * This method does not care about operator precedence.
+     */
+    public void genExpression(Type type, boolean change) {
+        if (change && generateInvalid()) type = getType();
+        if (!(type instanceof TypeInt) && type != TYPE_FLT) {
+            genUnary(type, false);
+            return;
+        }
+        var num = randLog(MAX_BINARY_EXPRESSIONS_PER_EXPRESSION);
+        while(num-->0) {
+            genUnary(type, false);
+            sb.append(BINARY_OP[random.nextInt(BINARY_OP.length)]);
+        }
+        genUnary(type, false);
+    }
+
+    /**
+     * Generate a unary expression.
+     */
+    public void genUnary(Type type, boolean change) {
+        if (change && generateInvalid()) type = getType();
+        if (!(type instanceof TypeInt) && type != TYPE_FLT) {
+            genSuffix(type, false);
+            return;
+        }
+        var num = randLog(MAX_UNARY_EXPRESSIONS_PER_EXPRESSION);
+        while(num-->0) {
+            sb.append(UNARY_OP[random.nextInt(UNARY_OP.length)]);
+        }
+        genSuffix(type, false);
+    }
+
+    public TypeStruct.Field getField(Type type) {
+        int n=0;
+        for (var s: structs) {
+            for (var f: s.fields) {
+                if (f.type.isa(type)) n++;
+            }
+        }
+        if (n==0) return null;
+        n = random.nextInt(n);
+        for (var s: structs) {
+            for (var f: s.fields) {
+                if (f.type.isa(type)) if (n--==0) return f;
+            }
+        }
+        throw new AssertionError();
+    }
+
+    /**
+     * Generate
+     */
+    public void genSuffix(Type type, boolean change) {
+        genSuffixRecursive(type, change, MAX_SUFFIX_RECURSIVE_DEPTH);
+    }
+
+    public void genSuffixRecursive(Type type, boolean change, int depth) {
+        if (change && generateInvalid()) type = getType();
+        if (depth > 0 && random.nextBoolean()) {
+            if (generateInvalid()) {
+                var field = getRandomName();
+                var t = getType();
+                genSuffixRecursive(t, true, depth-1);
+                sb.append(".").append(field);
+                return;
+            } else {
+                var field = getField(type);
+                if (field != null) {
+                    genSuffixRecursive(field.struct, true, depth-1);
+                    sb.append(".").append(field.name);
+                    return;
+                }
+            }
+        }
+        genPrimary(type, false);
+    }
+
+    /**
+     * Generate a primary expression.
+     */
+    public void genPrimary(Type type, boolean change) {
+        if (change && generateInvalid()) type = getType();
+        var rand = random.nextInt(10);
+        if (rand == 0 && exprDepth != 0) {
+            sb.append("(");
+            exprDepth--;
+            genExpression(type, false);
+            exprDepth++;
+            sb.append(")");
+        } else if (rand < 6) {
+            genVariable(type);
+        } else {
+            genConst(type);
+        }
+    }
+
+    /**
+     * Generate a constant.
+     */
+    public void genConst(Type type) {
+        if (generateInvalid()) type = getType();
+        if (type instanceof TypeInt || (type == TYPE_FLT && random.nextBoolean())) {
+            var rand = random.nextInt(10);
+            switch (rand) {
+                case 0 -> sb.append("true");
+                case 1 -> sb.append("false");
+                default -> sb.append(random.nextInt(1<<(rand-2)));
+            }
+        } else if (type == TYPE_FLT) {
+            sb.append(random.nextFloat());
+        } else if (type instanceof TypeNullable n) {
+            if ((n.base instanceof TypeStruct s && s.fields == null) || random.nextBoolean()) {
+                sb.append("null");
+            } else {
+                sb.append("new ").append(generateInvalid() ? getRandomName() : n.base.name);
+            }
+        } else {
+            sb.append("new ").append(generateInvalid() ? getRandomName() : type.name);
+        }
+    }
+
+    /**
+     * Generate a variable. If there are none generate a number instead.
+     * If the program is allowed to be invalid a random name can be generated in some cases.
+     */
+    public void genVariable(Type type) {
+        if (generateInvalid()) {
+            sb.append(getRandomName());
+            return;
+        }
+        if (generateInvalid()) type = getType();
+        var t = type;
+        var v = findVisibleVariablesMatching(va->va.type.isa(t));
+        if (v == null) genConst(type);
+        else sb.append(v.name);
+    }
+
+}
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn.smp b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn.smp
new file mode 100644
index 00000000..188e0a9f
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn.smp
@@ -0,0 +1,15 @@
+
+struct Person {
+  int age;
+};
+
+val fcn = { Person?[] ps, int x ->
+  val tmp = ps[x];
+  if( ps[x] )
+    ps[x].age++;
+};
+
+Person?[] !ps = new Person?[2];
+ps[0] = new Person;
+ps[1] = new Person;
+fcn(ps,1);
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn2.smp b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn2.smp
new file mode 100644
index 00000000..049132d9
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn2.smp
@@ -0,0 +1,5 @@
+
+val fcn = (arg&1)
+    ? { int x -> x*x; }
+    : { int x -> x+x; };
+fcn(arg);
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn3.smp b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn3.smp
new file mode 100644
index 00000000..a64564f0
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/progs/fcn3.smp
@@ -0,0 +1,42 @@
+
+//val fact = { int n -> n <= 1 ? 1 : fact(n-1)*n; }
+struct LL { LL? next; int payload; };
+
+
+struct String {
+
+    val _hashCodeString = { ->
+        int hash=0;
+        for( int i=0; i< cs#; i++ )
+            hash = hash*31 + cs[i];
+        if( !hash ) hash = 123456789;
+        return hash;
+    };
+
+    val equals = { String s ->
+        if( self == s ) return true;
+        if( cs# != s.cs# ) return false;
+        for( int i=0; i< #; i++ )
+            if( [i] != s.cs[i] )
+                return false;
+        return true;
+    };
+
+    int _hashCode = hash();
+    u8[] cs;
+};
+
+
+
+val hashCode= { String self ->
+    int hash = self._hashCode
+    ? self._hashCode
+    : self._hashCode = _hashCodeString(self);
+    return hash;
+};
+
+
+String s = new String { cs = new u8[17]; };
+s.cs[0] =  67; // C
+s.cs[1] = 108; // l
+hashCode(s);
diff --git a/chapter20/src/test/java/com/seaofnodes/simple/progs/sieve.smp b/chapter20/src/test/java/com/seaofnodes/simple/progs/sieve.smp
new file mode 100644
index 00000000..0788e6c5
--- /dev/null
+++ b/chapter20/src/test/java/com/seaofnodes/simple/progs/sieve.smp
@@ -0,0 +1,32 @@
+
+int[] !ary = new int[arg], !primes = new int[arg];
+int nprimes = 0, p=2;
+// Find primes while p^2 < arg
+while( p*p < arg ) {
+    // skip marked non-primes
+    while( ary[p]==1 ) p = p + 1;
+    // p is now a prime
+    primes[nprimes] = p;  nprimes = nprimes + 1;
+    // Mark out the rest non-primes
+    int i = p + p;
+    while( i < ary# ) {
+        ary[i] = 1;
+        i = i + p;
+    }
+    p = p + 1;
+}
+// Now just collect the remaining primes, no more marking
+while( p < arg ) {
+    if( ary[p] == 0 ) {
+        primes[nprimes] = p;  nprimes = nprimes + 1;
+    }
+    p = p + 1;
+}
+// Copy/shrink the result array
+int[] !rez = new int[nprimes];
+int j = 0;
+while( j < nprimes ) {
+    rez[j] = primes[j];
+    j = j + 1;
+}
+return rez;