From 86339c69320760c5b1acae681b9938d4c9f897f6 Mon Sep 17 00:00:00 2001
From: Cliff Click <cliffc@acm.org>
Date: Mon, 14 Sep 2026 09:08:05 -0700
Subject: Refinement on guard removal

Fix keep/unkeep balance.
Always fuzz small.
---
 chapter25/src/main/java/com/seaofnodes/simple/Parser.java    |  3 ++-
 .../src/main/java/com/seaofnodes/simple/node/PhiNode.java    | 12 ++++++++----
 .../src/test/java/com/seaofnodes/simple/FuzzerWrap.java      | 10 +++++++---
 3 files changed, 17 insertions(+), 8 deletions(-)

(limited to 'chapter25/src')

diff --git a/chapter25/src/main/java/com/seaofnodes/simple/Parser.java b/chapter25/src/main/java/com/seaofnodes/simple/Parser.java
index 2b6e5ddf..5453ee05 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/Parser.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/Parser.java
@@ -849,8 +849,9 @@ public class Parser {
         // Immediately fail e.g. `arg ? 7 : ptr`
         ParseException err;
         if( !fside.equals("else") && (err=ret.err()) !=null ) throw err;
+        ret.keep();
         r.peephole();
-        return ret;
+        return ret.unkeep();
     }
 
     /**
diff --git a/chapter25/src/main/java/com/seaofnodes/simple/node/PhiNode.java b/chapter25/src/main/java/com/seaofnodes/simple/node/PhiNode.java
index 4112a977..70f678cb 100644
--- a/chapter25/src/main/java/com/seaofnodes/simple/node/PhiNode.java
+++ b/chapter25/src/main/java/com/seaofnodes/simple/node/PhiNode.java
@@ -144,19 +144,23 @@ public class PhiNode extends Node {
             return null;
         if( !(r.in(3-nzIdx) instanceof CProjNode z && z._idx==1 && z.ctrl()==iff) )
             return null;
-        Node n = cast.in(1);
-        while( n instanceof GuardNode guard ) {
+        // Predicate was guarded?
+        Node n = cast.in(1), tested = null;
+        while( true ) {
+            if( iff.pred()==n ) tested = n;
+            if( !(n instanceof GuardNode guard && guard._nonZero) ) break;
             n = guard.in(1);
-            throw Utils.TODO("test and remove TODO");
         }
         CFGNode early = CFGNode.earlyCFG(n);
-        return iff.pred()==cast.in(1) && (early==null || early.dominates(r)) ? n : null;
+        return tested!=null && (early==null || early.dominates(r)) ? n : null;
     }
 
     // Same op on all Phi paths; all ops have only the Phi as a use.
     // None have a control input.
     private boolean same_op() {
         Node busy=null;
+        if( in(1) instanceof ConstantNode )
+            return false;
         for( int i=1; i<nIns(); i++ ) {
             Node op = in(i);
             if( in(1).getClass() != op.getClass() || op.in(0)!=null || in(1).nIns() != op.nIns() )
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/FuzzerWrap.java b/chapter25/src/test/java/com/seaofnodes/simple/FuzzerWrap.java
index a4532eb2..3aaa290a 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/FuzzerWrap.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/FuzzerWrap.java
@@ -20,12 +20,16 @@ public class FuzzerWrap {
         -6359653295501938199L, // monotonicity, escape is dead
          6506797708065910879L, // missing ModeNode._mode is optimistic
           650692970082394944L, // recursive bulk mem split
+         8335100609598232836L, // ternary result killed by region cleanup
+         2520958273643234516L, // nested guard merge
+        -3772838984504063325L, // fuzzer regression
     };
 
     private static final long[] OPEN_FAILING_SEEDS = {
-        8335100609598232836L,
-        2520958273643234516L,
-        -3772838984504063325L,
+        -4628356252269023530L,
+        -4022199781524079249L,
+        8824787517620928178L,
+        -673501011619761901L,
     };
 
 
-- 
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