Remove dead code

Clarify several TODO's as "Should not reach here"

30 files changed, 36 insertions, 308 deletions

diff --git a/chapter25/src/main/java/com/seaofnodes/simple/Parser.java b/chapter25/src/main/java/com/seaofnodes/simple/Parser.java
index 98093a77..e87fec35 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/Parser.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/Parser.java
@@ -999,9 +999,6 @@ public class Parser {
         // Auto-widen array to i64 (cast ptr to raw int bits)
         if( t == TypeInteger.BOT && expr._type instanceof TypeMemPtr tmp && tmp._obj.isAry() )
             return peep(new AddNode(peep(new PtrToIntNode(expr)),off(tmp._obj,"[]")));
-        // Null check has to eventually pass
-        if( t == Type.NIL && expr._type instanceof TypeMemPtr tmp && tmp.notNull() )
-           return peep(new CheckCastNode(t,null,expr));
         // Widen ints to floats, narrow wide types
         return peep(new ConvertNode(t,expr));
     }
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java
index bcefe996..a83b82a1 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java
@@ -84,7 +84,8 @@ public class CodeGen {
         assert _compunits.size()==1;
         for( CompUnit cu : _compunits.values() )
             return cu;
-        throw Utils.TODO();
+        assert false : "no compilation unit";
+        return null;
     }
 
     // True when fidx is published through a public field of a public class.
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/ElfExpr.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/ElfExpr.java
deleted file mode 100644
index 9d9b8a1c..00000000
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/ElfExpr.java
+++ /dev/null
@@ -1,87 +0,0 @@
-package com.seaofnodes.simple.codegen;
-
-import java.io.FileOutputStream;
-import java.io.IOException;
-import java.nio.ByteBuffer;
-import java.nio.ByteOrder;
-
-public class ElfExpr {
-    public static void main(String[] args) {
-        try (FileOutputStream fos = new FileOutputStream("hello.o")) {
-            ByteBuffer buffer = ByteBuffer.allocate(512);
-            buffer.order(ByteOrder.LITTLE_ENDIAN);
-
-            // === ELF HEADER (64 bytes) ===
-            buffer.put(new byte[]{
-                    0x7F, 'E', 'L', 'F',  // ELF Magic
-                    2, 1, 1, 0,          // 64-bit, little-endian, version
-                    0, 0, 0, 0, 0, 0, 0,  // ABI padding
-                    2, 0,                // Type: Executable (ET_EXEC)
-                    0x3E, 0x00,          // Machine: x86-64
-                    1, 0, 0, 0,          // ELF version
-                    0x00, 0x40, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // Entry point
-                    0, 0, 0, 0, 0, 0, 0, 0,  // Program header offset
-                    64, 0, 0, 0, 0, 0, 0, 0,  // Section header offset
-                    0, 0, 0, 0,            // Flags
-                    64, 0,                 // ELF header size
-                    0, 0,                   // Program header entry size
-                    0, 0,                   // Number of program header entries
-                    40, 0,                  // Section header entry size
-                    2, 0,                   // Number of section headers
-                    1, 0                    // Section header string table index
-            });
-
-            // === .TEXT SECTION (Executable Code) ===
-            byte[] textSection = {
-                    // sys_write (write(1, message, 13))
-                    (byte) 0x48, (byte) 0xC7, (byte) 0xC0, 0x01, 0x00, 0x00, 0x00,  // mov rax, 1
-                    (byte) 0x48, (byte) 0xC7, (byte) 0xC7, 0x01, 0x00, 0x00, 0x00,  // mov rdi, 1
-                    (byte) 0x48, (byte) 0xBE, (byte)0x90, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, // mov rsi, message
-                    (byte) 0x48, (byte) 0xC7, (byte) 0xC2, 0x0D, 0x00, 0x00, 0x00,  // mov rdx, 13
-                    (byte) 0x0F, (byte) 0x05,  // syscall
-
-                    // sys_exit (exit(0))
-                    (byte) 0x48, (byte) 0xC7, (byte) 0xC0, 0x3C, 0x00, 0x00, 0x00,  // mov rax, 60
-                    (byte) 0x48, (byte) 0x31, (byte) 0xFF,  // xor rdi, rdi
-                    (byte) 0x0F, (byte) 0x05   // syscall
-            };
-
-            // Append section data
-            buffer.position(256);
-            buffer.put(textSection);
-
-            // === STRING MESSAGE (.data Section) ===
-            byte[] message = "Hello, World!\n".getBytes();
-            buffer.position(400);
-            buffer.put(message);
-
-            // === SECTION HEADERS ===
-            buffer.position(64);
-
-            // Null Section (required as first entry)
-            buffer.put(new byte[40]);
-
-            // .text Section
-            buffer.putInt(1);    // Offset in section string table (".text")
-            buffer.putInt(1);    // Type: SHT_PROGBITS
-            buffer.putLong(6);   // Flags: Executable | Allocatable
-            buffer.putLong(0);   // Virtual address
-            buffer.putLong(256); // Offset to section data
-            buffer.putLong(textSection.length); // Section size
-            buffer.putInt(0);    // Link
-            buffer.putInt(0);    // Info
-            buffer.putLong(4);   // Address alignment
-            buffer.putLong(0);   // No extra entries
-
-            // === SECTION HEADER STRING TABLE ===
-            buffer.position(500);
-            buffer.put(".text".getBytes());
-            buffer.put((byte) 0x00);  // Null terminator
-
-            fos.write(buffer.array());
-            System.out.println("ELF object file 'hello.o' created.");
-        } catch (IOException e) {
-            e.printStackTrace();
-        }
-    }
-}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/IFG.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/IFG.java
index 2b559a38..e4e9dd69 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/IFG.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/IFG.java
@@ -224,9 +224,7 @@ abstract public class IFG {
         selfConflict(alloc,n,lrg,TMP.get(lrg));
     }
     private static void selfConflict(RegAlloc alloc, Node n, LRG lrg, Node prior) {
-        // Casts never produce a *new* value, just lift our understanding of the value.
-        // They do not force self-conflicts.
-        if( prior!=null && prior != n && !(n instanceof CheckCastNode) ) {
+        if( prior!=null && prior != n ) {
             lrg.selfConflict(prior);
             lrg.selfConflict(n);
             alloc.fail(lrg); // 2 unrelated values live at once same live range; self-conflict
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
index 0d5b9e7b..6650b19c 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/RegAlloc.java
@@ -753,6 +753,6 @@ public class RegAlloc {
             if( lrg(n)!=null && lrg(n)._reg == defreg )
                 return false;   // Clobbered
         }
-        throw Utils.TODO();
+        throw Utils.TODO("Should not reach here");
     }
 }
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/codegen/Serialize.java b/chapter25/src/main/java/com/seaofnodes/simple/codegen/Serialize.java
index 7c230f9c..ee5c48df 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/codegen/Serialize.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/codegen/Serialize.java
@@ -438,10 +438,6 @@ abstract public class Serialize {
         for( Node n : code._start._outputs ) {
             if( n instanceof ConstantNode con && !visit.get(con._nid) ) {
                 for( Node use : con.outs() ) {
-                    // Special case for Cast:BOT which is basically a double-indirect constant
-                    if( use instanceof CheckCastNode cast && cast.in(0)==null )
-                        for( Node useuse : cast.outs() )
-                            conUsed(cast,useuse,visit,cons);
                     // PtrToInt is another zero-code value rooted at a global
                     // constant.  Its array-body Add is the value used by the
                     // function, so include that extra link in the ownership
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/CheckCastMach.java b/chapter25/src/main/java/com/seaofnodes/simple/node/CheckCastMach.java
deleted file mode 100644
index 9943c7b4..00000000
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/CheckCastMach.java
+++ /dev/null
@@ -1,20 +0,0 @@
-package com.seaofnodes.simple.node;
-
-import com.seaofnodes.simple.codegen.CodeGen;
-import com.seaofnodes.simple.codegen.Encoding;
-import com.seaofnodes.simple.codegen.RegMask;
-import com.seaofnodes.simple.type.Type;
-import com.seaofnodes.simple.util.SB;
-
-/**
- * Cast a pointer to read-only
- */
-public class CheckCastMach extends CheckCastNode implements MachNode {
-    public CheckCastMach( CheckCastNode n ) { super(n); }
-    @Override public String op() { return label(); }
-    @Override public RegMask regmap(int i) { assert i==1; return RegMask.FULL; }
-    @Override public RegMask outregmap() { return RegMask.FULL; }
-    @Override public int twoAddress( ) { return in(1)._type==Type.BOTTOM ? 0 : 1; }
-    @Override public void encoding( Encoding enc ) { }
-    @Override public void asm(CodeGen code, SB sb) { sb.p(code.reg(in(1))); }
-}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/CheckCastNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/CheckCastNode.java
deleted file mode 100644
index 900ee70e..00000000
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/CheckCastNode.java
+++ /dev/null
@@ -1,82 +0,0 @@
-package com.seaofnodes.simple.node;
-
-import com.seaofnodes.simple.Parser;
-import com.seaofnodes.simple.type.*;
-import com.seaofnodes.simple.util.BAOS;
-
-import java.util.BitSet;
-import java.util.HashMap;
-import java.util.IdentityHashMap;
-
-// Upcast (join) the input to a t.  Used after guard test to lift an input.
-// Can also be used to make a type-assertion if ctrl is null.
-public class CheckCastNode extends TypeNode {
-    public CheckCastNode(Type t, Node ctrl, Node in) { super(t,ctrl, in); }
-
-    public CheckCastNode(CheckCastNode c) {
-        super(c);               // Call parent copy constructor
-        setType(compute());     // Ensure type is recomputed
-    }
-    @Override public Tag serialTag() { return Tag.CheckCast; }
-    @Override public void packed( BAOS baos, HashMap<String,Integer> strs, HashMap<Type,Integer> types, IdentityHashMap<Node, Integer> anodes ) {
-        baos.packed2(types.get(_con)); // NPE if fails lookup
-    }
-    static Node make( BAOS bais, Type[] types)  { return new CheckCastNode(types[bais.packed2()], null, null); }
-
-    @Override public String label() { return "("+_con.str()+")"; }
-
-    @Override
-    public String uniqueName() { return "CheckCast_" + _nid; }
-
-    @Override public boolean isPinned() { return in(0)!=null; }
-
-    @Override
-    public StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        return in(1)._print0(sb.append(label()), visited);
-    }
-
-    @Override
-    public Type compute() {
-        // Cast array to int
-        Type t1 = in(1)._type;
-        if( _con == TypeInteger.BOT && t1 instanceof TypeMemPtr tmp && tmp._obj.isAry() )
-            return _con;
-
-        // If unconditional, it must collapse (or error)
-        if( in(0)==null )
-            return _con;
-        // If conditional, return the join.  The guard test ensures
-        // the join is correct.
-        return t1.join(_con);
-    }
-
-    @Override
-    public Node idealize() {
-        return in(1)._type.isa(_con) ? in(1) : null;
-    }
-
-    @Override
-    public Parser.ParseException err() {
-        // Has a condition to test, so OK
-        if( in(0) != null ) return null;
-        if( in(1)._type != Type.BOTTOM )
-            // No condition to test, so this must optimize away
-            return Parser.error( "Type " + in(1)._type.str() + " is not of declared type " + _con.str(), null );
-        // Only happens for un-initialized refs that must init.
-        // Allow uses of initializing stores, but other uses represent a
-        // partially initialized field, and should error
-        boolean bad = false;
-        StoreNode init=null;
-        for( Node use : _outputs )
-            if( (use instanceof StoreNode st && st._init && !((TypeMemPtr)st.ptr()._type)._obj._name.startsWith("class") ) )
-                init = st;
-            else if( (use instanceof StoreNode st && st.val() instanceof CheckCastNode cast && cast.in(1)._type == Type.BOTTOM) )
-                /*bogus init store in constructor*/;
-            else bad = true;
-        if( !bad ) return null;
-        if( init==null ) return null; // Error somewhere else
-        // Expecting an init store
-        TypeMemPtr ptr = (TypeMemPtr)init.ptr()._type;
-        throw Parser.error("'"+ptr._obj._name+"' is not fully initialized, field '" + init._name + "' is only partially set in the constructor", init._loc);
-    }
-}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/LoadNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/LoadNode.java
index 4ff2bd82..73c288e6 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/LoadNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/LoadNode.java
@@ -192,7 +192,6 @@ public class LoadNode extends MemOpNode {
                 case CallEndNode cend: addDep(mproj); break outer; // TODO: Bypass no-alias call
                 default: throw Utils.TODO();
                 }
-            case CheckCastNode cast: mem = cast.in(1); break;
             case MemMergeNode merge:  mem = merge.alias(_alias);  break;
             case EscapeNode esc:
                 if( esc.self()==ptr ) // Proved equal
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/MachConcreteNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/MachConcreteNode.java
index 9440a7ea..c2dcae0b 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/MachConcreteNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/MachConcreteNode.java
@@ -1,7 +1,6 @@
 package com.seaofnodes.simple.node;
 
 import com.seaofnodes.simple.type.Type;
-import com.seaofnodes.simple.util.Utils;
 import java.io.ByteArrayOutputStream;
 import java.util.BitSet;
 
@@ -13,8 +12,8 @@ public abstract class MachConcreteNode extends Node implements MachNode {
     public MachConcreteNode(Node[]nodes) { super(nodes); }
 
     @Override public String label() { return op(); }
-    @Override public Type compute () { throw Utils.TODO(); }
-    @Override public Node idealize() { throw Utils.TODO(); }
+    @Override public Type compute () { throw new AssertionError("Do not call compute on "+getClass().getSimpleName()); }
+    @Override public Node idealize() { throw new AssertionError("Do not call idealize on "+getClass().getSimpleName()); }
 
     @Override public StringBuilder _print1(StringBuilder sb, BitSet visited) {
         sb.append("(").append(op()).append(",");
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
index e4e7d607..aad3e677 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
@@ -133,8 +133,6 @@ public class MemMergeNode extends Node {
         // Fold defaults into the default
         boolean progress=false, allDefault=true;
         for( int i=2; i<nIns(); i++ ) {
-            if( in(i) instanceof CheckCastNode cast )
-                { setDef(i,cast.in(1)); progress=true; }
             if( in(1) == in(i) && in(1) != null ) { setDef(i,null); progress=true; }
             else                                  { allDefault=false; }
         }
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/Node.java b/chapter25/src/main/java/com/seaofnodes/simple/node/Node.java
index 1ce8382a..27f41cff 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/Node.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/Node.java
@@ -79,12 +79,12 @@ public abstract class Node implements Cloneable {
     // Disk/serialized opcode tags
     public enum Tag {
         Add,And,EQ,NE,LT,LE,ULT,
-        CallEnd,Call,CheckCast,ConFldOff,Con,CProj,
+        CallEnd,Call,ConFldOff,Con,CProj,
         Div,Escape,Extern,Fun,FunPtr,If,Load,Loop,
         MemMerge,Minus,Mul,
         New,Never,Not,Or,Parm,Phi,Proj,
         ReadOnly,Return,Region,RoundF32,
-        Sar,Shl,Shr,Start,Stop,Store,Struct,Sub,ToFloat,
+        Sar,Shl,Shr,Start,Stop,Store,Sub,ToFloat,
         XCtrl,Xor,StartCU,StopCU,Guard,MemPhi,BulkMemPhi,PtrToInt;
         public static final Tag[] VALS = values();
         public Node make( BAOS bais, String[] strs, Type[] types, GlobalBits fileAliases, GlobalBits aliases ) {
@@ -121,7 +121,6 @@ public abstract class Node implements Cloneable {
 
             case Call  ->      CallNode.make(bais);
             case CallEnd->  CallEndNode.make(bais     ,types);
-            case CheckCast -> CheckCastNode.make(bais,types);
             case CProj ->     CProjNode.make(bais,strs);
             case Con   ->  ConstantNode.make(bais     ,types);
             case Escape->    EscapeNode.make(bais     ,types);
@@ -140,7 +139,6 @@ public abstract class Node implements Cloneable {
             case Stop ->       StopNode.make(bais);
             case StartCU->  StartCUNode.make(bais,strs,types);
             case StopCU ->   StopCUNode.make(bais);
-            case Struct->    StructNode.make(bais,     types);
             case Region->    RegionNode.make(bais);
 
             default -> throw Utils.TODO();
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/PtrToIntNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/PtrToIntNode.java
index d781620b..02f77f36 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/PtrToIntNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/PtrToIntNode.java
@@ -10,10 +10,9 @@ import java.util.BitSet;
 /**
  * Reinterpret a non-null managed pointer as its raw integer address.
  *
- * This node changes representation families but emits no code.  In particular,
- * it is not a {@link CheckCastNode}: no control-dependent proof can turn a
- * pointer into an integer.  Array-to-C-pointer conversion adds the array body
- * offset separately.
+ * This node changes representation families but emits no code.  No
+ * control-dependent proof can turn a pointer into an integer; array-to-C-pointer
+ * conversion adds the array body offset separately.
  */
 public class PtrToIntNode extends Node {
     public PtrToIntNode(Node ptr) { super(null,ptr); }
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/StoreNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/StoreNode.java
index bd268af2..04fbc781 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/StoreNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/StoreNode.java
@@ -110,8 +110,6 @@ public class StoreNode extends MemOpNode {
 
     @Override
     public Node idealize() {
-        assert !(mem() instanceof CheckCastNode);
-
         // Freeze the semantic Store variant as soon as the pointer exposes a
         // canonical field declaration.  Waiting until after structural memory
         // peeps can lose the declaration to a flow-sensitive constant field
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/StructNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/StructNode.java
deleted file mode 100644
index 4dcc695f..00000000
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/StructNode.java
+++ /dev/null
@@ -1,60 +0,0 @@
-package com.seaofnodes.simple.node;
-
-import com.seaofnodes.simple.type.*;
-import com.seaofnodes.simple.util.BAOS;
-import com.seaofnodes.simple.util.Utils;
-import java.util.BitSet;
-import java.util.HashMap;
-import java.util.IdentityHashMap;
-
-/**
- * Build a compound object
- */
-public class StructNode extends Node {
-
-    public final TypeStruct _ts;
-    public StructNode(TypeStruct ts) { _ts=ts; assert !ts._open; }
-    @Override public Tag serialTag() { return Tag.Struct; }
-    @Override public void packed( BAOS baos, HashMap<String,Integer> strs, HashMap<Type,Integer> types, IdentityHashMap<Node, Integer> anodes ) {
-        //baos.packed1(nIns());
-        //baos.packed2(_label==null ? 0 : strs.get(_label));
-        //baos.packed2(types.get(_type)); // Write _type not _minType, which can be higher
-        throw Utils.TODO();
-    }
-    static Node make( BAOS bais, Type[] types)  {
-        //Node[] ins = new Node[bais.packed1()];
-        //return new StructNode(types[bais.packed2()], ins);
-        throw Utils.TODO();
-    }
-
-    @Override
-    public StringBuilder _print1(StringBuilder sb, BitSet visited) {
-        if( _ts==null ) return sb.append("STRUCT?");
-        sb.append(_ts._name).append(" {  ");
-        for( int i=0; i<nIns(); i++ ) {
-            sb.append(_ts._fields[i]._fname).append(":");
-            sb.append(in(i)==null ? Type.BOTTOM : in(i)._type);
-            sb.append("; ");
-        }
-        sb.setLength(sb.length()-2);
-        return sb.append("}");
-    }
-
-    @Override
-    public TypeStruct compute() {
-        if( _ts==null ) return TypeStruct.BOT;
-        Field[] fs = new Field[_ts._fields.length];
-        for( int i=0; i<fs.length; i++ )
-            fs[i] = _ts._fields[i].makeFrom(in(i)==null ? Type.TOP : in(i)._type);
-        return TypeStruct.make(_ts._name,false,fs);
-    }
-
-    @Override
-    public Node idealize() { return null; }
-
-    @Override
-    public boolean eq(Node n) { return _ts == ((StructNode)n)._ts; }
-
-    @Override
-    int hash() { return _ts==null ? 0 : _ts.hashCode(); }
-}
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/MemOpARM.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/MemOpARM.java
index 08bdf974..25402018 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/MemOpARM.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/MemOpARM.java
@@ -4,7 +4,6 @@ import com.seaofnodes.simple.codegen.*;
 import com.seaofnodes.simple.node.*;
 import com.seaofnodes.simple.type.*;
 import com.seaofnodes.simple.util.SB;
-import com.seaofnodes.simple.util.Utils;
 import java.lang.StringBuilder;
 import java.util.BitSet;
 
@@ -36,8 +35,8 @@ public abstract class MemOpARM extends MemOpNode implements MachNode {
 
     @Override public  StringBuilder _printMach(StringBuilder sb, BitSet visited) { return sb.append(".").append(_name); }
 
-    @Override public Type compute() { throw Utils.TODO(); }
-    @Override public Node idealize() { throw Utils.TODO(); }
+    @Override public Type compute() { throw new AssertionError("Do not call compute on "+getClass().getSimpleName()); }
+    @Override public Node idealize() { throw new AssertionError("Do not call idealize on "+getClass().getSimpleName()); }
 
     int size() { return _bytes; }
 
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
index 852fbdb1..20343fb4 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
@@ -685,7 +685,6 @@ public class arm extends Machine {
         case AndNode and     -> and(and);
         case BoolNode bool   -> cmp(bool);
         case CallNode call   -> call(call);
-        case CheckCastNode cast -> new CheckCastMach(cast);
         case PtrToIntNode ptr -> new PtrToIntMach(ptr);
         case GuardNode guard -> new GuardMach(guard);
         case CallEndNode cend-> new CallEndMach(cend);
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/riscv/MemOpRISC.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/riscv/MemOpRISC.java
index 79f22fb8..5fcba6f8 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/riscv/MemOpRISC.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/riscv/MemOpRISC.java
@@ -27,8 +27,8 @@ public abstract class MemOpRISC extends MemOpNode implements MachNode {
 
     @Override public StringBuilder _printMach(StringBuilder sb, BitSet visited) { return sb.append(".").append(_name); }
 
-    @Override public Type compute() { throw Utils.TODO(); }
-    @Override public Node idealize() { throw Utils.TODO(); }
+    @Override public Type compute() { throw new AssertionError("Do not call compute on "+getClass().getSimpleName()); }
+    @Override public Node idealize() { throw new AssertionError("Do not call idealize on "+getClass().getSimpleName()); }
 
     // func3 is based on load/store size and extend
     abstract int func3();
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java
index 078a7693..27141d21 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java
@@ -335,7 +335,6 @@ public class riscv extends Machine {
         case AndNode      and -> and(and);
         case BoolNode    bool -> cmp(bool);
         case CallNode    call -> call(call);
-        case CheckCastNode cast -> new CheckCastMach(cast);
         case PtrToIntNode  ptr -> new PtrToIntMach(ptr);
         case GuardNode guard  -> new GuardMach(guard);
         case CallEndNode cend -> new CallEndMach(cend);
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MemOpX86.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MemOpX86.java
index bfaf7a91..87cc6e35 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MemOpX86.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/MemOpX86.java
@@ -4,7 +4,6 @@ import com.seaofnodes.simple.codegen.*;
 import com.seaofnodes.simple.node.*;
 import com.seaofnodes.simple.type.*;
 import com.seaofnodes.simple.util.SB;
-import com.seaofnodes.simple.util.Utils;
 import java.lang.StringBuilder;
 import java.util.BitSet;
 
@@ -59,8 +58,8 @@ public abstract class MemOpX86 extends MemOpNode implements MachNode {
     }
 
     @Override public String label() { return op(); }
-    @Override public Type compute() { throw Utils.TODO(); }
-    @Override public Node idealize() { throw Utils.TODO(); }
+    @Override public Type compute() { throw new AssertionError("Do not call compute on "+getClass().getSimpleName()); }
+    @Override public Node idealize() { throw new AssertionError("Do not call idealize on "+getClass().getSimpleName()); }
 
     // Register mask allowed on input i.
     @Override public RegMask regmap(int i) {
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
index 4cabefca..5b70834c 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
@@ -376,7 +376,6 @@ public class x86_64_v2 extends Machine {
         case CProjNode      c -> new CProjNode(c);
         case CallEndNode cend -> new CallEndMach(cend);
         case CallNode    call -> call(call);
-        case CheckCastNode cast -> new CheckCastMach(cast);
         case PtrToIntNode  ptr -> new PtrToIntMach(ptr);
         case GuardNode  guard -> new GuardMach(guard);
         case ConstantNode con -> con(con);
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/print/JSViewer.java b/chapter25/src/main/java/com/seaofnodes/simple/print/JSViewer.java
index 0f34af2e..204b2642 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/print/JSViewer.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/print/JSViewer.java
@@ -256,7 +256,6 @@ public class JSViewer implements AutoCloseable {
         return switch( n ) {
         case CFGNode cfg  -> "yellow";
         case NewNode nnn  -> "lightgreen";
-        case StructNode s -> "lightgreen";
         default -> typeColor(n._type);
         };
     }
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/type/Type.java b/chapter25/src/main/java/com/seaofnodes/simple/type/Type.java
index 509326bb..fbbfbada 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/type/Type.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/type/Type.java
@@ -229,8 +229,8 @@ public class Type /*implements Cloneable*/ {
     }
 
     // At/Set child at 'idx' to t
-    public Type at( int idx ) { throw Utils.TODO(); }
-    public void set( int idx, Type t ) { throw Utils.TODO(); }
+    public Type at( int idx ) { throw Utils.TODO("Should not reach here: type has no children"); }
+    public void set( int idx, Type t ) { throw Utils.TODO("Should not reach here: type has no children"); }
     public int nkids() { return 0; }   // Number of kids
 
 
@@ -322,7 +322,7 @@ public class Type /*implements Cloneable*/ {
             case TXCTRL-> TCTRL;
             case TNIL  -> TXNIL;
             case TXNIL -> TNIL;
-        default -> throw Utils.TODO(); // Should not reach here
+        default -> throw Utils.TODO("Should not reach here: unknown simple type");
         });
     }
 
@@ -548,7 +548,7 @@ public class Type /*implements Cloneable*/ {
         case TCTRL -> CONTROL;
         case TXCTRL->XCONTROL;
         case TNIL  -> NIL;
-        default -> throw Utils.TODO();
+        default -> throw Utils.TODO("Should not reach here: unknown simple type tag");
         };
     }
 
@@ -572,7 +572,7 @@ public class Type /*implements Cloneable*/ {
         case TFLD    ->   Field      .packed( off, bais, strs );
         case TSTRUCT ->   TypeStruct .packed( off, bais, strs );
         case TTUPLE  ->   TypeTuple  .packed( off, bais );
-        default -> throw Utils.TODO();
+        default -> throw Utils.TODO("Should not reach here: unknown packed type tag");
         };
     }
 
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeConAry.java b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeConAry.java
index 2a0a817e..29e65c94 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeConAry.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeConAry.java
@@ -43,7 +43,7 @@ public abstract class TypeConAry<A> extends TypeScalar {
                 return ti.meet(e);
             return this;
         }
-        throw Utils.TODO();
+        throw Utils.TODO("Should not reach here: constant array meet with non-element type");
     }
 
     @Override public boolean isHigh() { return this==TOP; }
@@ -65,10 +65,10 @@ public abstract class TypeConAry<A> extends TypeScalar {
     }
     // Generic element _type
     public int elemT() { return TBOT; }
-    public long at8(int idx) { throw Utils.TODO(); }
-    public int len() { throw Utils.TODO(); }
-    @Override public int log_size() { throw Utils.TODO(); }
-    public void write( BAOS baos ) { throw Utils.TODO(); }
+    public long at8(int idx) { throw Utils.TODO("Should not reach here: abstract constant array has no elements"); }
+    public int len() { throw Utils.TODO("Should not reach here: abstract constant array has no length"); }
+    @Override public int log_size() { throw Utils.TODO("Should not reach here: abstract constant array has no element size"); }
+    public void write( BAOS baos ) { throw Utils.TODO("Should not reach here: abstract constant array cannot be written"); }
 
     // Reserve tags for u8 array
     @Override int TAGOFF() { return 1; }
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeFloat.java b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeFloat.java
index 1325b707..d410e9cf 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeFloat.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeFloat.java
@@ -53,7 +53,7 @@ public class TypeFloat extends TypeScalar {
         case   0 -> ""+_con+((float)_con==_con ? "f" : "");
         case  32 ->  "f32";
         case  64 ->  "flt";
-        default  -> throw Utils.TODO();
+        default  -> throw Utils.TODO("Should not reach here: unknown float size");
         };
     }
     private boolean isF32() { return ((float)_con)==_con; }
@@ -116,7 +116,7 @@ public class TypeFloat extends TypeScalar {
         case 0 -> F64;
         case 1 -> F32;
         case 2 -> constant(Double.longBitsToDouble(bais.packed8()));
-        default -> throw Utils.TODO();
+        default -> throw Utils.TODO("Should not reach here: unknown float type tag");
         };
     }
 
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeInteger.java b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
index c981f3d3..28e788fe 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeInteger.java
@@ -203,7 +203,7 @@ public class TypeInteger extends TypeScalar {
         case 4 -> ZERO;
         case 5 -> constant(bais.packed8());
         case 6 -> make(bais.packed8(),bais.packed8(),(byte)(bais.packed1()-3));
-        default -> throw Utils.TODO();
+        default -> throw Utils.TODO("Should not reach here: unknown integer type tag");
         };
     }
 
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeMem.java b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeMem.java
index 7658e3fd..c634aab0 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeMem.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeMem.java
@@ -150,7 +150,7 @@ public class TypeMem extends Type {
     @Override public TypeMem makeZero() { return TOP; }
     @Override public boolean isHigh() { return _t.isHigh(); }
     @Override boolean _isConstant() { return _one && _clz && _alias!= 1 && _t._isConstant(); }
-    @Override public int log_size() { throw Utils.TODO(); }
+    @Override public int log_size() { throw Utils.TODO("Should not reach here: memory has no scalar storage size"); }
     @Override boolean _isFinal() { return _t._isFinal(); }
     @Override TypeMem _makeStorage() { return make(_alias,_t._makeStorage(),_one,_clz,_final,_escFs,_escAs); }
 
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/type/TypePtr.java b/chapter25/src/main/java/com/seaofnodes/simple/type/TypePtr.java
index 7b27ff2b..38941ed1 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/type/TypePtr.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/type/TypePtr.java
@@ -26,7 +26,7 @@ public class TypePtr extends TypeNil {
 
     public static void gather(ArrayList<Type> ts) { ts.add(PTR); ts.add(NPTR); }
 
-    TypeNil makeFrom(byte nil) { throw Utils.TODO(); }
+    TypeNil makeFrom(byte nil) { throw Utils.TODO("Should not reach here: plain pointer nil state is canonical"); }
 
     @Override public TypeNil xmeet(Type t) {
         TypePtr that = (TypePtr) t;
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeStruct.java b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeStruct.java
index 2949b015..e2011b38 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeStruct.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeStruct.java
@@ -469,7 +469,7 @@ public class TypeStruct extends Type {
 
     // log_size for a struct is not defined, unless its exactly some power of
     // 2.  *Total size* is well-defined, and is available in the offsets.
-    @Override public int log_size() { throw Utils.TODO(); }
+    @Override public int log_size() { throw Utils.TODO("Should not reach here: structs have no scalar log size"); }
     @Override public int size() { return offset(_fields.length); }
     @Override public int alignment() {
         int align = 0;
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeTuple.java b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeTuple.java
index 86f8aef1..075698dc 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/type/TypeTuple.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/type/TypeTuple.java
@@ -94,9 +94,9 @@ public class TypeTuple extends Type {
                 return false;
         return true;
     }
-    @Override boolean _isFinal() { throw Utils.TODO(); }
+    @Override boolean _isFinal() { throw Utils.TODO("Should not reach here: tuples are not stored object values"); }
 
-    @Override TypeMemPtr _makeRO() { throw Utils.TODO(); }
+    @Override TypeMemPtr _makeRO() { throw Utils.TODO("Should not reach here: tuples cannot be made read-only"); }
 
     @Override Type _upgradeType(HashMap<String,Type> TYPES) {
         Type[] ts = new Type[_types.length];
@@ -105,7 +105,7 @@ public class TypeTuple extends Type {
         return make(ts);
     }
 
-    @Override public int log_size() { throw Utils.TODO(); }
+    @Override public int log_size() { throw Utils.TODO("Should not reach here: tuples have no scalar storage size"); }
     @Override public int alignment() {
         assert isConstant();
         int align = 0;