Handle infinite loops

Loop tree building (and breaking infinite loops) needs to happen *before* instruction selection, which is optional.  Best done as a new compiler phase... which now wants a driver.
Add a compiler driver; adjust tests to use.
Add "never-branch" handling to the 3 CPU port main branch ops.

27 files changed, 246 insertions, 124 deletions

diff --git a/chapter21/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java b/chapter21/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java
index 114d0b5c..fb46a6a2 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/codegen/CodeGen.java
@@ -20,6 +20,7 @@ public class CodeGen {
         Parse,                  // Parse ASCII text into Sea-of-Nodes IR
         Opto,                   // Run ideal optimizations
         TypeCheck,              // Last check for bad programs
+        LoopTree,               // Build a loop tree; break infinite loops
         InstSelect,             // Convert to target hardware nodes
         Schedule,               // Global schedule (code motion) nodes
         LocalSched,             // Local schedule
@@ -49,6 +50,28 @@ public class CodeGen {
         P = new Parser(this,arg);
     }
 
+
+    // All passes up to Phase, except ELF
+    public CodeGen driver( Phase phase ) { return driver(phase,null,null); }
+    public CodeGen driver( Phase phase, String cpu, String callingConv ) {
+        if( _phase==null )                       parse();
+        if( _phase.ordinal() < phase.ordinal() ) opto();
+        if( _phase.ordinal() < phase.ordinal() ) typeCheck();
+        if( _phase.ordinal() < phase.ordinal() ) loopTree();
+        if( _phase.ordinal() < phase.ordinal() && cpu != null ) instSelect(cpu,callingConv);
+        if( _phase.ordinal() < phase.ordinal() ) GCM();
+        if( _phase.ordinal() < phase.ordinal() ) localSched();
+        if( _phase.ordinal() < phase.ordinal() ) regAlloc();
+        if( _phase.ordinal() < phase.ordinal() ) encode();
+        return this;
+    }
+
+    // Run all the phases through final ELF emission
+    public CodeGen driver( String cpu, String callingConv, String obj ) throws IOException {
+        return driver(Phase.Encoding,cpu,callingConv).exportELF(obj);
+    }
+
+
     // ---------------------------
     /**
      *  A counter, for unique node id generation.  Starting with value 1, to
@@ -172,18 +195,30 @@ public class CodeGen {
         return this;
     }
 
+    // ---------------------------
+    // Build the loop tree; break never-exit loops
+    public int _tLoopTree;
+    public CodeGen loopTree() {
+        assert _phase.ordinal() <= Phase.TypeCheck.ordinal();
+        _phase = Phase.LoopTree;
+        long t0 = System.currentTimeMillis();
+        // Build the loop tree, fix never-exit loops
+        _start.buildLoopTree(_stop);
+        _tLoopTree = (int)(System.currentTimeMillis() - t0);
+        return this;
+    }
 
     // ---------------------------
     // Code generation CPU target
     public Machine _mach;
-    //
+    // Chosen calling convention (usually either Win64 or SystemV)
     public String _callingConv;
 
     // Convert to target hardware nodes
     public int _tInsSel;
     public CodeGen instSelect( String cpu, String callingConv ) { return instSelect(cpu,callingConv,PORTS); }
     public CodeGen instSelect( String cpu, String callingConv, String base ) {
-        assert _phase.ordinal() <= Phase.TypeCheck.ordinal();
+        assert _phase.ordinal() == Phase.LoopTree.ordinal();
         _phase = Phase.InstSelect;
 
         _callingConv = callingConv;
@@ -261,8 +296,6 @@ public class CodeGen {
         _phase = Phase.Schedule;
         long t0 = System.currentTimeMillis();
 
-        // Build the loop tree, fix never-exit loops
-        _start.buildLoopTree(_stop);
         GlobalCodeMotion.buildCFG(this);
         _tGCM = (int)(System.currentTimeMillis() - t0);
         if( show )
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/CFGNode.java b/chapter21/src/main/java/com/seaofnodes/simple/node/CFGNode.java
index 0b97c574..0aeee5f3 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/CFGNode.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/CFGNode.java
@@ -57,7 +57,7 @@ public abstract class CFGNode extends Node {
 
     // Used by the encoding / final BB layout
     public CFGNode uctrlSkipEmpty() {
-        CFGNode x = this, y=null;
+        CFGNode x = this, y;
         while( x.nOuts() == 1 && (y=x.uctrl())!=null ) // Skip empty blocks
             x = y;
         return x;
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/IfNode.java b/chapter21/src/main/java/com/seaofnodes/simple/node/IfNode.java
index f00f4f9f..9bb269d5 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/IfNode.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/IfNode.java
@@ -21,7 +21,9 @@ public class IfNode extends CFGNode implements MultiNode {
     @Override
     public StringBuilder _print1(StringBuilder sb, BitSet visited) {
         sb.append("if( ");
-        return in(1)._print0(sb, visited).append(" )");
+        if( in(1)==null ) sb.append("never");
+        else in(1)._print0(sb, visited);
+        return sb.append(" )");
     }
 
     public Node ctrl() { return in(0); }
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/LoopNode.java b/chapter21/src/main/java/com/seaofnodes/simple/node/LoopNode.java
index 778f2a8d..847a4aa0 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/LoopNode.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/LoopNode.java
@@ -51,7 +51,7 @@ public class LoopNode extends RegionNode {
             : CodeGen.CODE._mach.never(back()); // Machine never-branch
         CProjNode t = new CProjNode(iff,0,"True" ).init();
         CProjNode f = new CProjNode(iff,1,"False").init();
-        setDef(2,t);
+        setDef(2,t);            // True continues loop, False (never) exits loop
         iff._ltree = t._ltree = _ltree;
         ReturnNode ret = fun.ret();
         f._ltree = ret._ltree;
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/NeverNode.java b/chapter21/src/main/java/com/seaofnodes/simple/node/NeverNode.java
index 1dcad1db..516f218b 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/NeverNode.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/NeverNode.java
@@ -9,6 +9,7 @@ import java.util.BitSet;
 
 // "Never true" for infinite loop exits
 public class NeverNode extends IfNode {
+    public NeverNode(NeverNode ctrl) { super(ctrl); }
     public NeverNode(Node ctrl) { super(ctrl,null); }
 
     @Override public String label() { return "Never"; }
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/PhiNode.java b/chapter21/src/main/java/com/seaofnodes/simple/node/PhiNode.java
index be31dd38..f0bf1166 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/PhiNode.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/PhiNode.java
@@ -90,6 +90,7 @@ public class PhiNode extends Node {
                     { solo=false; break; }
             if( solo ) {
                 Node cp = op.copy();
+                cp._type = null;    // Fresh type
                 cp.addDef(null);    // No control
 
                 for( int j=1; j<op.nIns(); j++ ) {
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/BranchARM.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/BranchARM.java
index d07c5cef..4b8bd687 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/BranchARM.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/BranchARM.java
@@ -16,6 +16,7 @@ public class BranchARM extends IfNode implements MachNode, RIPRelSize {
 
     @Override public void postSelect(CodeGen code) {
         Node set = in(1);
+        if( set==null ) return; // Never-node cutout
         Node cmp = set.in(1);
         // Bypass an expected Set and just reference the cmp directly
         if( set instanceof SetARM)
@@ -31,13 +32,19 @@ public class BranchARM extends IfNode implements MachNode, RIPRelSize {
     @Override public void encoding( Encoding enc ) {
         // Assuming that condition flags are already set.  These flags are set
         // by comparison (or sub).  No need for regs because it uses flags
+        if( in(1)!=null ) {
+            // B.cond
+            enc.add4( arm.b_cond(arm.OP_BRANCH, 0, arm.make_condition(_bop)) );
+        } else {
+            if( _bop=="!=" ) return; // Inverted, no code
+            enc.add4(arm.b(arm.OP_UJMP, 0));
+        }
         enc.jump(this,cproj(0));
-        // B.cond
-        enc.add4( arm.b_cond(arm.OP_BRANCH, 0, arm.make_condition(_bop)) );
     }
 
     // Delta is from opcode start
     @Override public byte encSize(int delta) {
+        if( in(1)==null && _bop=="!=" ) return 0; // Inverted never-node, no code
         if( -(1<<19) <= delta && delta < (1<<19) ) return 4;
         // 2 word encoding needs a tmp register, must teach RA
         throw Utils.TODO();
@@ -45,6 +52,7 @@ public class BranchARM extends IfNode implements MachNode, RIPRelSize {
 
     // Delta is from opcode start
     @Override public void patch( Encoding enc, int opStart, int opLen, int delta ) {
+        assert !( in(1)==null && _bop=="!=" ); // Inverted never-node, no code no patch
         if( opLen==4 ) {
             enc.patch4(opStart,arm.b_cond(arm.OP_BRANCH, delta, arm.make_condition(_bop)));
         } else {
@@ -53,8 +61,13 @@ public class BranchARM extends IfNode implements MachNode, RIPRelSize {
     }
 
     @Override public void asm(CodeGen code, SB sb) {
-        String src = code.reg(in(1));
-        if( src!="flags" ) sb.p(src).p(" ");
+        if( in(1)!=null ) {     // Never-node
+            String src = code.reg(in(1));
+            if( src!="flags" ) sb.p(src).p(" ");
+        } else if( _bop=="!=" ) {
+            sb.p("never");
+            return;
+        }
         CFGNode prj = cproj(0).uctrlSkipEmpty();
         if( !prj.blockHead() ) prj = prj.cfg0();
         sb.p(label(prj));
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/FunARM.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/FunARM.java
index b919df66..028688b7 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/FunARM.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/FunARM.java
@@ -1,7 +1,8 @@
 package com.seaofnodes.simple.node.cpus.arm;
 
-import com.seaofnodes.simple.codegen.*;
 import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.codegen.*;
 import com.seaofnodes.simple.node.FunNode;
 import com.seaofnodes.simple.node.MachNode;
 
@@ -27,12 +28,14 @@ public class FunARM  extends FunNode implements MachNode {
         // Can be negative if the stack args passed are never referenced
         int sz = Math.max(_maxSlot - _maxArgSlot,0);
         sz = ((sz+1) & -2)+1;   // Pad to 16
-        if( _frameAdjust != 0 )
-            enc.add4(arm.imm_inst(arm.OPI_ADD, (_frameAdjust*8)&0xFFF, arm.RSP, arm.RSP));
+        _frameAdjust = (short)sz;
+        if( sz == 0 ) return;   // Skip if no frame adjust
+        if( sz*-8 < -1L<<12 ) throw Utils.TODO();
+        enc.add4(arm.imm_inst(arm.OPI_ADD, (_frameAdjust*-8)&0xFFF, arm.RSP, arm.RSP));
     }
 
     @Override public void asm(CodeGen code, SB sb) {
         if( _frameAdjust != 0 )
-            sb.p("rsp += #").p(_frameAdjust*8);
+            sb.p("rsp -= #").p(_frameAdjust*8);
     }
 }
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/SplitARM.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/SplitARM.java
index 684cc167..50ba2274 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/SplitARM.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/SplitARM.java
@@ -1,7 +1,9 @@
 package com.seaofnodes.simple.node.cpus.arm;
 
+import com.seaofnodes.simple.SB;
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.codegen.*;
+import com.seaofnodes.simple.node.FunNode;
 import com.seaofnodes.simple.node.Node;
 import com.seaofnodes.simple.node.SplitNode;
 import com.seaofnodes.simple.node.cpus.riscv.riscv;
@@ -55,4 +57,10 @@ public class SplitARM extends SplitNode {
             enc.add4(arm.f_mov_general(arm.OP_FMOV, 0b01, 0, 0b110, src - arm.D_OFFSET, dst));
         }
     }
+
+    // General form: "mov  dst = src"
+    @Override public void asm(CodeGen code, SB sb) {
+        FunNode fun = code._encoding==null ? null : code._encoding._fun;
+        sb.p(code.reg(this,fun)).p(" = ").p(code.reg(in(1),fun));
+    }
 }
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
index bedda4e2..97c0cf15 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/arm/arm.java
@@ -679,9 +679,11 @@ public class arm extends Machine {
         // If/Bool combos will match to a Cmp/Set which sets flags.
         // Most general arith ops will also set flags, which the Jmp needs directly.
         // Loads do not set the flags, and will need an explicit TEST
-        if( !(iff.in(1) instanceof BoolNode) )
-            iff.setDef(1,new BoolNode.EQ(iff.in(1),new ConstantNode(TypeInteger.ZERO)));
-        return new BranchARM(iff, invert(((BoolNode)iff.in(1)).op()));
+        String op = "!=";
+        if( iff.in(1) instanceof BoolNode bool ) op = bool.op();
+        else if( iff.in(1)==null ) op = "=="; // Never-node cutout
+        else iff.setDef(1, new BoolNode.NE(iff.in(1), new ConstantNode(TypeInteger.ZERO)));
+        return new BranchARM(iff, op);
     }
 
     private Node add(AddNode add) {
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/BranchRISC.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/BranchRISC.java
index 438ba760..6b1568f2 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/BranchRISC.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/BranchRISC.java
@@ -39,15 +39,21 @@ public class BranchRISC extends IfNode implements MachNode, RIPRelSize {
     }
 
     @Override public void encoding( Encoding enc ) {
+        if( in(1)==null && _bop=="!=" ) return; // Inverted never-node, no code
         enc.jump(this,cproj(0));
-        // Todo: relocs (for offset - immf)
-        short src1 = enc.reg(in(1));
-        short src2 = in(2)==null ? (short)riscv.ZERO : enc.reg(in(2));
-        enc.add4(riscv.b_type(riscv.OP_BRANCH, riscv.jumpop(_bop), src1, src2, 0));
+        if( in(1)==null )       // Never node
+            enc.add4(riscv.j_type(riscv.OP_JAL, 0, 0));
+        else {
+            // Todo: relocs (for offset - immf)
+            short src1 = enc.reg(in(1));
+            short src2 = in(2)==null ? (short)riscv.ZERO : enc.reg(in(2));
+            enc.add4(riscv.b_type(riscv.OP_BRANCH, riscv.jumpop(_bop), src1, src2, 0));
+        }
     }
 
     // Delta is from opcode start
     @Override public byte encSize(int delta) {
+        if( in(1)==null && _bop=="!=" ) return 0; // Inverted never-node, no code
         if( -4*1024 <= delta && delta < 4*1024 ) return 4;
         // 2 word encoding needs a tmp register, must teach RA
         throw Utils.TODO();
@@ -55,16 +61,25 @@ public class BranchRISC extends IfNode implements MachNode, RIPRelSize {
 
     // Delta is from opcode start
     @Override public void patch( Encoding enc, int opStart, int opLen, int delta ) {
-        short src1 = enc.reg(in(1));
-        short src2 = in(2)==null ? (short)riscv.ZERO : enc.reg(in(2));
-        if( opLen==4 ) {
-            enc.patch4(opStart,riscv.b_type(riscv.OP_BRANCH, riscv.jumpop(_bop), src1, src2, delta));
+        assert !( in(1)==null && _bop=="!=" ); // Inverted never-node, no code no patch
+        if( in(1)==null ) {     // Never node
+            enc.patch4(opStart,riscv.j_type(riscv.OP_JAL, 0, delta));
         } else {
-            throw Utils.TODO();
+            short src1 = enc.reg(in(1));
+            short src2 = in(2)==null ? (short)riscv.ZERO : enc.reg(in(2));
+            if( opLen==4 ) {
+                enc.patch4(opStart,riscv.b_type(riscv.OP_BRANCH, riscv.jumpop(_bop), src1, src2, delta));
+            } else {
+                throw Utils.TODO();
+            }
         }
     }
 
     @Override public void asm(CodeGen code, SB sb) {
+        if( in(1)==null && _bop=="!=" ) {
+            sb.p("never");
+            return;
+        }
         String src1 = in(1)==null ? "#0" : code.reg(in(1));
         String src2 = in(2)==null ? "#0" : code.reg(in(2));
         sb.p(src1).p(" ").p(_bop).p(" ").p(src2).p(" ");
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/FunRISC.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/FunRISC.java
index 5f888806..43a9439e 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/FunRISC.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/FunRISC.java
@@ -1,7 +1,8 @@
 package com.seaofnodes.simple.node.cpus.riscv;
 
-import com.seaofnodes.simple.codegen.*;
 import com.seaofnodes.simple.SB;
+import com.seaofnodes.simple.Utils;
+import com.seaofnodes.simple.codegen.*;
 import com.seaofnodes.simple.node.FunNode;
 import com.seaofnodes.simple.node.MachNode;
 
@@ -27,12 +28,14 @@ public class FunRISC extends FunNode implements MachNode {
         // Can be negative if the stack args passed are never referenced
         int sz = Math.max(_maxSlot - _maxArgSlot,0);
         sz = ((sz+1) & -2)+1;   // Pad to 16
-        if( _frameAdjust != 0 )
-            enc.add4(riscv.i_type(riscv.OP_IMM, riscv.SP, 0, riscv.SP, (_frameAdjust*-8) & 0xFFF));
+        _frameAdjust = (short)sz;
+        if( sz == 0 ) return; // Skip if no frame adjust
+        if( sz*-8 < -1L<<12 ) throw Utils.TODO();
+        enc.add4(riscv.i_type(riscv.OP_IMM, riscv.SP, 0, riscv.SP, (_frameAdjust*-8) & 0xFFF));
     }
 
     @Override public void asm(CodeGen code, SB sb) {
         if( _frameAdjust != 0 )
-            sb.p("rsp += #").p(_frameAdjust*-8);
+            sb.p("rsp -= #").p(_frameAdjust*8);
     }
 }
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/SplitRISC.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/SplitRISC.java
index ebf2d5b9..bd50842c 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/SplitRISC.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/SplitRISC.java
@@ -1,7 +1,9 @@
 package com.seaofnodes.simple.node.cpus.riscv;
 
+import com.seaofnodes.simple.SB;
 import com.seaofnodes.simple.Utils;
 import com.seaofnodes.simple.codegen.*;
+import com.seaofnodes.simple.node.FunNode;
 import com.seaofnodes.simple.node.Node;
 import com.seaofnodes.simple.node.SplitNode;
 
@@ -54,6 +56,11 @@ public class SplitRISC extends SplitNode {
             //fmv.x.d
             enc.add4(riscv.r_type(riscv.OP_FP, dst, 0, src - riscv.F_OFFSET, 0, 0b1110001));
         }
+    }
 
+    // General form: "mov  dst = src"
+    @Override public void asm(CodeGen code, SB sb) {
+        FunNode fun = code._encoding==null ? null : code._encoding._fun;
+        sb.p(code.reg(this,fun)).p(" = ").p(code.reg(in(1),fun));
     }
 }
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java
index 5b2ea9b9..e526252e 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/riscv/riscv.java
@@ -496,7 +496,7 @@ public class riscv extends Machine {
             return new BranchRISC(iff, bop, bool.in(1), bool.in(2));
         }
         // Vs zero
-        return new BranchRISC(iff, "!=", iff.in(1), null);
+        return new BranchRISC(iff, iff.in(1)==null ? "==" : "!=", iff.in(1), null);
     }
 
     private Node or(OrNode or) {
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/FunX86.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/FunX86.java
index a0747025..9f6fc715 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/FunX86.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/FunX86.java
@@ -40,6 +40,7 @@ public class FunX86 extends FunNode implements MachNode {
     }
 
     @Override public void asm(CodeGen code, SB sb) {
-        sb.p("rsp -= #").p(_frameAdjust*8);
+        if( _frameAdjust!=0 )
+            sb.p("rsp -= #").p(_frameAdjust*8);
     }
 }
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/JmpX86.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/JmpX86.java
index d77d4acd..51e7f061 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/JmpX86.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/JmpX86.java
@@ -15,6 +15,7 @@ public class JmpX86 extends IfNode implements MachNode, RIPRelSize {
     @Override public String label() { return op(); }
     @Override public void postSelect(CodeGen code) {
         Node set = in(1);
+        if( set==null ) return; // Never-node cutout
         Node cmp = set.in(1);
         // Bypass an expected Set and just reference the cmp directly
         if( set instanceof SetX86 setx && (cmp instanceof CmpX86 || cmp instanceof CmpIX86 || cmp instanceof CmpMemX86 || cmp instanceof CmpFX86) ) {
@@ -28,35 +29,48 @@ public class JmpX86 extends IfNode implements MachNode, RIPRelSize {
     @Override public void invert() { _bop = invert(_bop);  }
 
     @Override public void encoding( Encoding enc ) {
+        if( in(1)!=null ) {
+            int op = x86_64_v2.jumpop(_bop);
+            enc.add1(op-16).add1(0); // Short form jump
+        } else {
+            if( _bop=="!=" ) return; // Inverted, no code
+            enc.add1(0xEB).add1(0);  // Never-node
+        }
         enc.jump(this,cproj(0));
-        int op = x86_64_v2.jumpop(_bop);
-        enc.add1(op-16);      // Short form jump
-        enc.add1(0);          // Offset
     }
 
     // Delta is from opcode start, but X86 measures from the end of the 2-byte encoding
-    @Override public byte encSize(int delta) { return (byte)(x86_64_v2.imm8(delta-2) ? 2 : 6); }
+    @Override public byte encSize(int delta) {
+        if( in(1)==null && _bop=="!=" ) return 0; // Inverted never-node, no code
+        return (byte)(x86_64_v2.imm8(delta-2) ? 2 : 6);
+    }
 
     // Delta is from opcode start
     @Override public void patch( Encoding enc, int opStart, int opLen, int delta ) {
+        assert !( in(1)==null && _bop=="!=" ); // Inverted never-node, no code no patch
         byte[] bits = enc.bits();
         if( opLen==2 ) {
-            assert bits[opStart] == x86_64_v2.jumpop(_bop)-16;
+            assert in(1)==null || bits[opStart] == x86_64_v2.jumpop(_bop)-16;
             delta -= 2;         // Offset from opcode END
             assert (byte)delta==delta;
             bits[opStart+1] = (byte)delta;
         } else {
-            assert bits[opStart] == x86_64_v2.jumpop(_bop)-16;
+            assert in(1)==null || bits[opStart] == x86_64_v2.jumpop(_bop)-16;
             delta -= 6;         // Offset from opcode END
             bits[opStart] = 0x0F;
-            bits[opStart+1] = (byte)x86_64_v2.jumpop(_bop);
+            bits[opStart+1] = (byte)(in(1)==null ? 0xE9 : x86_64_v2.jumpop(_bop));
             enc.patch4(opStart+2,delta);
         }
     }
 
     @Override public void asm(CodeGen code, SB sb) {
-        String src = code.reg(in(1));
-        if( src!="flags" ) sb.p(src).p(" ");
+        if( in(1)!=null ) {     // Never-node
+            String src = code.reg(in(1));
+            if( src!="flags" ) sb.p(src).p(" ");
+        } else if( _bop=="!=" ) {
+            sb.p("never");
+            return;
+        }
         CFGNode prj = cproj(0).uctrlSkipEmpty(); // 0 is True is jump target
         if( !prj.blockHead() ) prj = prj.cfg0();
         sb.p(label(prj));
diff --git a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
index 12b3a12c..401a9b2c 100644
--- a/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
+++ b/chapter21/src/main/java/com/seaofnodes/simple/node/cpus/x86_64_v2/x86_64_v2.java
@@ -5,8 +5,6 @@ import com.seaofnodes.simple.codegen.*;
 import com.seaofnodes.simple.node.*;
 import com.seaofnodes.simple.type.*;
 
-import java.io.ByteArrayOutputStream;
-
 public class x86_64_v2 extends Machine {
     public x86_64_v2( CodeGen code ) {}
     // X86-64 V2.  Includes e.g. SSE4.2 and POPCNT.
@@ -79,7 +77,7 @@ public class x86_64_v2 extends Machine {
         case ">"  -> 0x8F;
         case "<"  -> 0x8C;
         case "<=" -> 0x8E;
-        case ">=" -> 0X8D;
+        case ">=" -> 0x8D;
         default -> throw new IllegalArgumentException("Too many arguments");
         };
     }
@@ -119,14 +117,6 @@ public class x86_64_v2 extends Machine {
         return rex;
     }
 
-    // return the size of the immediate
-    public static int imm_size(long imm) {
-        if(imm8(imm)) return 8;
-        if(imm16(imm)) return 16;
-        if(imm32(imm)) return 32;
-        return 64;
-    }
-
     public static int rex(int reg, int ptr, int idx) {
         return rex(reg, ptr, idx, true);
     }
@@ -421,10 +411,10 @@ public class x86_64_v2 extends Machine {
         case AddNode add -> add(add);
         case AndNode and -> and(and);
         case BoolNode bool -> cmp(bool);
+        case CProjNode c -> new CProjNode(c);
         case CallEndNode cend -> new CallEndX86(cend);
         case CallNode call -> call(call);
         case CastNode cast -> new CastX86(cast);
-        case CProjNode c -> new CProjNode(c);
         case ConstantNode con -> con(con);
         case DivFNode divf -> new DivFX86(divf);
         case DivNode div -> new DivX86(div);
@@ -451,6 +441,7 @@ public class x86_64_v2 extends Machine {
         case SubFNode subf -> new SubFX86(subf);
         case SubNode sub -> sub(sub);
         case ToFloatNode tfn -> i2f8(tfn);
+        case XCtrlNode x -> new ConstantNode(Type.XCONTROL);
         case XorNode xor -> xor(xor);
 
         case LoopNode loop -> new LoopNode(loop);
@@ -460,7 +451,7 @@ public class x86_64_v2 extends Machine {
     }
 
     public static boolean imm8( long imm ) { return -128 <= imm && imm <= 127; }
-    public static boolean imm16(long imm) {return -32768 <= imm && imm <= 32767; }
+
     public static boolean imm32( long imm ) { return (int)imm==imm; }
 
     // Attempt a full LEA-style break down.
@@ -595,10 +586,11 @@ public class x86_64_v2 extends Machine {
         // If/Bool combos will match to a Cmp/Set which sets flags.
         // Most general arith ops will also set flags, which the Jmp needs directly.
         // Loads do not set the flags, and will need an explicit TEST
-        BoolNode bool;
-        if( iff.in(1) instanceof BoolNode bool0 ) bool = bool0;
-        else iff.setDef(1, bool=new BoolNode.NE(iff.in(1), new ConstantNode(TypeInteger.ZERO)));
-        return new JmpX86(iff, bool.op());
+        String op = "!=";
+        if( iff.in(1) instanceof BoolNode bool ) op = bool.op();
+        else if( iff.in(1)==null ) op = "=="; // Never-node cutout
+        else iff.setDef(1, new BoolNode.NE(iff.in(1), new ConstantNode(TypeInteger.ZERO)));
+        return new JmpX86(iff, op);
     }
 
     private Node ld(LoadNode ld) {
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter11Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter11Test.java
index c2b9a86d..7e88b60e 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter11Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter11Test.java
@@ -289,7 +289,7 @@ else {
 }
 """);
         code.parse().opto().typeCheck().GCM();
-        assertEquals("return Phi(Region,9,Top,Top,Top,Top);", code.print());
+        assertEquals("return 9;", code.print());
     }
 
 
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter18Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter18Test.java
index 99daae7d..c0e28412 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter18Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter18Test.java
@@ -1,5 +1,6 @@
 package com.seaofnodes.simple;
 
+import com.seaofnodes.simple.codegen.CodeGen.Phase;
 import com.seaofnodes.simple.codegen.CodeGen;
 import org.junit.Ignore;
 import org.junit.Test;
@@ -14,7 +15,7 @@ public class Chapter18Test {
 """
 return 0;
 """);
-        code.parse().opto().typeCheck().GCM().localSched();
+        code.driver(Phase.LocalSched);
         assertEquals("return 0;", code._stop.toString());
         assertEquals("0", Eval2.eval(code,  2));
     }
@@ -76,7 +77,7 @@ var sq = { int x ->
 };
 return sq(arg)+sq(3);
 """);
-        code.parse().opto().typeCheck().GCM().localSched();
+        code.driver(Phase.LocalSched);
         assertEquals("Stop[ return (#2+#2); return (Parm_x(sq,int)*x); ]", code._stop.toString());
         assertEquals("13", Eval2.eval(code, 2));
     }
@@ -174,7 +175,7 @@ for(;;) {
     i2i = id(x);
 }
 """);
-        code.parse().opto().typeCheck().GCM().localSched();
+        code.driver(Phase.LocalSched);
         assertEquals("Stop[ return #2; return Parm_i(x,int); ]", code._stop.toString());
         assertEquals("3", Eval2.eval(code,  0));
     }
@@ -190,7 +191,7 @@ for(;;) {
     arg = x(3);
 }
 """);
-        code.parse().opto().typeCheck().GCM().localSched();
+        code.driver(Phase.LocalSched);
         assertEquals("return Top;", code._stop.toString());
         assertEquals("null", Eval2.eval(code,  0));
     }
@@ -215,7 +216,7 @@ ps[0] = new Person;
 ps[1] = new Person;
 fcn(ps,1);
 """);
-        code.parse().opto().typeCheck().GCM().localSched();
+        code.driver(Phase.LocalSched);
         assertEquals("return 0;", code._stop.toString());
         assertEquals("0", Eval2.eval(code,  0));
     }
@@ -345,7 +346,7 @@ if (arg) i2i = null;
 if (i2i) return i2i(arg);
 return f2f(o)(1);
 """);
-        code.parse().opto().typeCheck().GCM().localSched();
+        code.driver(Phase.LocalSched);
         assertEquals("Stop[ return Phi(Region,#2,#2); return Parm_i(o,int); ]", code._stop.toString());
         assertEquals("1", Eval2.eval(code,  2));
     }
@@ -361,7 +362,7 @@ Person !p = new Person;
 p.coffee_count += 1;
 return p.coffee_count;
 """);
-        code.parse().opto().typeCheck().GCM().localSched();
+        code.driver(Phase.LocalSched);
         assertEquals("return 1;", code._stop.toString());
         assertEquals("1", Eval2.eval(code,  2));
     }
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter19Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter19Test.java
index 9ba8e972..787dfd4c 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter19Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter19Test.java
@@ -1,5 +1,6 @@
 package com.seaofnodes.simple;
 
+import com.seaofnodes.simple.codegen.CodeGen.Phase;
 import com.seaofnodes.simple.codegen.CodeGen;
 import java.io.IOException;
 import java.nio.file.Files;
@@ -32,98 +33,98 @@ return 0;
 
     @Test
     public void testBasic0() {
-        CodeGen code = new CodeGen("return 0;").parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        CodeGen code = new CodeGen("return 0;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg+1;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return -17;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg==1;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg<<1;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg >> 1;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg >>> 1;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg / 2;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg * 6;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg & 2;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg | 2;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg ^ 2;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        CodeGen code = new CodeGen("return arg + 2.0;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return (addf,(cvtf,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();
+        CodeGen code = new CodeGen("return arg - 2.0;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return (subf,(cvtf,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();
+        CodeGen code = new CodeGen("return arg * 2.0;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return (mulf,(cvtf,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();
+        CodeGen code = new CodeGen("return arg / 2.0;").driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return (mulf,(cvtf,arg),0.5f);", code._stop.toString());
     }
 
@@ -133,7 +134,7 @@ return 0;
 """
 int arg1 =  arg + 1;
 return arg1 / arg;""");
-        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return (div,(inc,arg),arg);", code._stop.toString());
     }
 
@@ -144,7 +145,7 @@ return arg1 / arg;""");
 int arg1 =  arg + 1;
 return arg1 * arg;
 """);
-        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return (mul,(inc,arg),arg);", code._stop.toString());
     }
 
@@ -154,7 +155,7 @@ return arg1 * arg;
 int a = arg;
 return a + 2.0;
 """
-        ).parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        ).driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return (addf,(cvtf,arg),2.0f);", code._stop.toString());
     }
 
@@ -169,7 +170,7 @@ else {
     a = arg-3;
 }
 return a;""");
-        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return Phi(Region,(addi,arg),(addi,arg));", code.print());
     }
 
@@ -184,7 +185,7 @@ if( arg==1 )
 else
     a=b+1;
 return a+b;""");
-        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return (add,(add,Phi(Region,(shli,arg),arg),arg),Phi(Region,4,5));", code.print());
     }
 
@@ -196,7 +197,7 @@ 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();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return Phi(Loop,0,(add,Phi_sum,Phi(Loop,0,(inc,Phi_i))));", code.print());
     }
 
@@ -206,42 +207,42 @@ return sum;""");
 """
 struct S { int a; S? c; };
 return new S;""");
-        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         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();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return .[];", code.print());
     }
 
@@ -258,7 +259,7 @@ 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();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return .[];", code.print());
     }
 
@@ -273,7 +274,7 @@ for( int i=0; i<A#; i++ )
 for( int i=0; i<A#; i++ )
     B[i] += A[i];
 """);
-        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return 0;", code.print());
     }
 
@@ -286,7 +287,7 @@ for( int i=0; i<A#; i++ )
     A[i]++;
 return A[1];
 """);
-        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return .[];", code.print());
     }
 
@@ -294,7 +295,7 @@ return A[1];
     public void testNewton() throws IOException {
         String src = Files.readString(Path.of("src/test/java/com/seaofnodes/simple/progs/newtonFloat.smp"))
             + "flt farg = arg;  return test_sqrt(farg);";
-        CodeGen code = new CodeGen(src).parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        CodeGen code = new CodeGen(src).driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return Phi(Loop,(cvtf,arg),(mulf,(addf,(divf,cvtf,Phi_guess),Phi_guess),0.5f));", code.print());
     };
 
@@ -302,7 +303,7 @@ return A[1];
     @Test
     public void sieveOfEratosthenes() throws IOException {
         String src = Files.readString(Path.of("src/test/java/com/seaofnodes/simple/progs/sieve.smp"));
-        CodeGen code = new CodeGen(src).parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        CodeGen code = new CodeGen(src).driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("return [u32];", code.print());
         //assertEquals("u32[ 2,3,5,7,11,13,17,19]",Eval2.eval(code, 20));
     }
@@ -315,7 +316,7 @@ return A[1];
 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();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("Stop[ return (add,#2,(muli,#2)); return (mul,Parm_x($fun1,int),x); return (shli,Parm_x($fun2,int)); ]", code.print());
     }
 
@@ -326,7 +327,7 @@ return fcn(2)*10 + fcn(3);
 val sq = { int x -> x*x; };
 return sq(arg) + sq(3);
 """);
-        code.parse().opto().typeCheck().instSelect("x86_64_v2", "SystemV").GCM().localSched();
+        code.driver(Phase.LocalSched,"x86_64_v2", "SystemV");
         assertEquals("Stop[ return (add,#2,#2); return (mul,Parm_x(sq,int),x); ]", code.print());
     }
 }
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter20Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter20Test.java
index 8b7136ab..664620a8 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter20Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter20Test.java
@@ -23,7 +23,7 @@ public class Chapter20Test {
 
     static void testCPU( String src, String cpu, String os, int spills, String stop ) {
         CodeGen code = new CodeGen(src);
-        code.parse().opto().typeCheck().instSelect(cpu,os).GCM().localSched().regAlloc();
+        code.driver(CodeGen.Phase.RegAlloc,cpu,os);
         int delta = spills>>3;
         if( delta==0 ) delta = 1;
         if( spills != -1 )
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Chapter21Test.java b/chapter21/src/test/java/com/seaofnodes/simple/Chapter21Test.java
index e584f9bc..259cbb4f 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Chapter21Test.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Chapter21Test.java
@@ -13,16 +13,15 @@ import static org.junit.Assert.*;
 public class Chapter21Test {
 
     @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));
+    public void testJig() throws IOException {
+        String src = Files.readString(Path.of("src/test/java/com/seaofnodes/simple/progs/jig.smp"));
+        testCPU(src,"x86_64_v2", "SystemV",1,null);
+        testCPU(src,"riscv"    , "SystemV",1,null);
+        testCPU(src,"arm"      , "SystemV",1,null);
     }
 
     static void testCPU( String src, String cpu, String os, int spills, String stop ) {
-        CodeGen code = new CodeGen(src);
-        code.parse().opto().typeCheck().instSelect(cpu,os).GCM().localSched().regAlloc().encode();
+        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.Encoding,cpu,os);
         int delta = spills>>3;
         if( delta==0 ) delta = 1;
         if( spills != -1 )
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/Simple.java b/chapter21/src/test/java/com/seaofnodes/simple/Simple.java
index 56761e7a..9b1e2827 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/Simple.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/Simple.java
@@ -16,11 +16,12 @@ public class Simple {
     static final int DUMP_AFTER_PARSE        = 1<<0;
     static final int DUMP_AFTER_OPTO         = 1<<1;
     static final int DUMP_AFTER_TYPE_CHECK   = 1<<2;
-    static final int DUMP_AFTER_INSTR_SELECT = 1<<3;
-    static final int DUMP_AFTER_GCM          = 1<<4;
-    static final int DUMP_AFTER_LOCAL_SCHED  = 1<<5;
-    static final int DUMP_AFTER_REG_ALLOC    = 1<<6;
-    static final int DUMP_AFTER_ENCODE       = 1<<7;
+    static final int DUMP_AFTER_LOOP_TREE    = 1<<3;
+    static final int DUMP_AFTER_INSTR_SELECT = 1<<4;
+    static final int DUMP_AFTER_GCM          = 1<<5;
+    static final int DUMP_AFTER_LOCAL_SCHED  = 1<<6;
+    static final int DUMP_AFTER_REG_ALLOC    = 1<<7;
+    static final int DUMP_AFTER_ENCODE       = 1<<8;
 
     static final int DUMP_FINAL              = 1<<16;
 
@@ -88,12 +89,13 @@ Options:
                     case DUMP_AFTER_PARSE        -> "01-parse.dot";
                     case DUMP_AFTER_OPTO         -> "02-opto.dot";
                     case DUMP_AFTER_TYPE_CHECK   -> "03-type_check.dot";
-                    case DUMP_AFTER_INSTR_SELECT -> "04-instr_select.dot";
-                    case DUMP_AFTER_GCM          -> "05-gcm.dot";
-                    case DUMP_AFTER_LOCAL_SCHED  -> "06-local_sched.dot";
-                    case DUMP_AFTER_REG_ALLOC    -> "07-reg_allos.dot";
-                    case DUMP_AFTER_ENCODE       -> "08-local_sched.dot";
-                    case DUMP_FINAL              -> "09-final.dot";
+                    case DUMP_AFTER_LOOP_TREE    -> "04-loop_tree.dot";
+                    case DUMP_AFTER_INSTR_SELECT -> "05-instr_select.dot";
+                    case DUMP_AFTER_GCM          -> "06-gcm.dot";
+                    case DUMP_AFTER_LOCAL_SCHED  -> "07-local_sched.dot";
+                    case DUMP_AFTER_REG_ALLOC    -> "08-reg_allos.dot";
+                    case DUMP_AFTER_ENCODE       -> "09-local_sched.dot";
+                    case DUMP_FINAL              -> "10-final.dot";
                     default                      -> throw Utils.TODO();
                 };
 
@@ -110,6 +112,7 @@ Options:
                         case DUMP_AFTER_PARSE        -> "After Parse:";
                         case DUMP_AFTER_OPTO         -> "After OPTO:";
                         case DUMP_AFTER_TYPE_CHECK   -> "After Type Check:";
+                        case DUMP_AFTER_LOOP_TREE    -> "After Loop Tree:";
                         case DUMP_AFTER_INSTR_SELECT -> "After Instruction Selection:";
                         case DUMP_AFTER_GCM          -> "After GCM:";
                         case DUMP_AFTER_LOCAL_SCHED  -> "After Local Scheduling:";
@@ -134,6 +137,8 @@ Options:
         System.out.println(String.format("Optimization Time:          %.3f sec", t));
         total += t = code._tTypeCheck / 1e3;
         System.out.println(String.format("Type Checking Time:         %.3f sec", t));
+        total += t = code._tLoopTree / 1e3;
+        System.out.println(String.format("Loop Tree Time:             %.3f sec", t));
         total += t = code._tInsSel / 1e3;
         System.out.println(String.format("Instruction Selection Time: %.3f sec", t));
         total += t = code._tGCM / 1e3;
@@ -180,6 +185,7 @@ loop:   for (int i = 0; i < args.length; i++) {
                     case "--dump-after-parse":        dump |= DUMP_AFTER_PARSE; break;
                     case "--dump-after-opto":         dump |= DUMP_AFTER_OPTO; break;
                     case "--dump-after-type-check":   dump |= DUMP_AFTER_TYPE_CHECK; break;
+                    case "--dump-after-loop-tree":    dump |= DUMP_AFTER_LOOP_TREE; break;
                     case "--dump-after-instr-select": dump |= DUMP_AFTER_INSTR_SELECT; break;
                     case "--dump-after-gcm":          dump |= DUMP_AFTER_GCM; break;
                     case "--dump-after-local-sched":  dump |= DUMP_AFTER_LOCAL_SCHED; break;
@@ -250,6 +256,9 @@ loop:   for (int i = 0; i < args.length; i++) {
         code.typeCheck();
         dump(code, dump, DUMP_AFTER_TYPE_CHECK);
 
+        code.loopTree();
+        dump(code, dump, DUMP_AFTER_LOOP_TREE);
+
         if (do_codegen) {
             code.instSelect(PORTS, cpu, abi);
             dump(code, dump, DUMP_AFTER_INSTR_SELECT);
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/TestC.java b/chapter21/src/test/java/com/seaofnodes/simple/TestC.java
index 2d908699..c6e0b196 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/TestC.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/TestC.java
@@ -49,7 +49,7 @@ public abstract class TestC {
         String bin = efile+xtn;
         String obj = bin+".o";
         // Compile simple, emit ELF
-        CodeGen code = new CodeGen(src).parse().opto().typeCheck().instSelect( CPU_PORT, simple_conv).GCM().localSched().regAlloc().encode().exportELF(obj);
+        CodeGen code = new CodeGen(src).driver( CPU_PORT, simple_conv, obj);
 
         // Compile the C program
         var params = new String[] {
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/TestRisc5.java b/chapter21/src/test/java/com/seaofnodes/simple/TestRisc5.java
index 275cdebb..9c64fe9f 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/TestRisc5.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/TestRisc5.java
@@ -18,7 +18,7 @@ public abstract class TestRisc5 {
     public static EvalRisc5 build( String dir, String file, int arg ) throws IOException {
         // Compile and export Simple
         String src = Files.readString(Path.of(dir+"/"+file+".smp"));
-        CodeGen code = new CodeGen(src).parse().opto().typeCheck().instSelect( "riscv", "SystemV").GCM().localSched().regAlloc().encode();
+        CodeGen code = new CodeGen(src).driver(CodeGen.Phase.Encoding,"riscv", "SystemV");
 
         // Image
         byte[] image = new byte[1<<20]; // A megabyte
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/fuzzer/FuzzerUtils.java b/chapter21/src/test/java/com/seaofnodes/simple/fuzzer/FuzzerUtils.java
index 669a1e6a..b90b663d 100644
--- a/chapter21/src/test/java/com/seaofnodes/simple/fuzzer/FuzzerUtils.java
+++ b/chapter21/src/test/java/com/seaofnodes/simple/fuzzer/FuzzerUtils.java
@@ -101,7 +101,7 @@ class FuzzerUtils {
             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();
+            return code.driver(CodeGen.Phase.LocalSched);
         } finally {
             System.setErr(err);
             System.setOut(out);
diff --git a/chapter21/src/test/java/com/seaofnodes/simple/progs/jig.smp b/chapter21/src/test/java/com/seaofnodes/simple/progs/jig.smp
new file mode 100644
index 00000000..47aeb2e5
--- /dev/null
+++ b/chapter21/src/test/java/com/seaofnodes/simple/progs/jig.smp
@@ -0,0 +1,17 @@
+// -*- mode: java;  -*-
+struct s0 {
+    bool v0;
+    u8 v2;
+    i16 v1;
+    byte v3;
+    int v4;
+    i16 v5;
+    int v6;
+};
+                    while(new s0.v1) {}
+            if(new s0.v6) return new s0.v5;
+                return new s0.v2;
+struct s1 {
+    int v7;
+};
+                while(new s1.v7) arg=new s0.v3;