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.

17 files changed, 154 insertions, 59 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) {