From 1e527b16b28f31b08cbb36b7b1bf2d689487a989 Mon Sep 17 00:00:00 2001
From: Cliff Click <cliffc@acm.org>
Date: Sun, 20 Sep 2026 17:46:47 -0700
Subject: Split self-conflict phis once at a loop head

if this works, saves a copy-per-loop.  If it fails, next round split as normal
---
 .../java/com/seaofnodes/simple/BrainFuckTest.java  |  2 +-
 .../java/com/seaofnodes/simple/Chapter24Test.java  |  2 ++
 .../simple/codegen/RegAllocTestSupport.java        | 28 ++++++++++++++++++++++
 3 files changed, 31 insertions(+), 1 deletion(-)

(limited to 'chapter25/src')

diff --git a/chapter25/src/test/java/com/seaofnodes/simple/BrainFuckTest.java b/chapter25/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
index a42ebc24..f3da1592 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/BrainFuckTest.java
@@ -77,7 +77,7 @@ val brain_fuck = { ->
         assertEquals(brain_fuck.length(),A5.ld4s(ptr_arm));
 
         for( int i=0; i<brain_fuck.length(); i++ )
-            assertEquals(brain_fuck.charAt(i), A5.ld1z(ptr+4+i));
+            assertEquals(brain_fuck.charAt(i), A5.ld1z(ptr_arm+4+i));
     }
 
 }
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/Chapter24Test.java b/chapter25/src/test/java/com/seaofnodes/simple/Chapter24Test.java
index 0abdfb3e..a94f36f2 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/Chapter24Test.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/Chapter24Test.java
@@ -12,6 +12,8 @@ import org.junit.Test;
 import static org.junit.Assert.*;
 
 public class Chapter24Test {
+    @Test public void testColdLoopSelfConflict() { com.seaofnodes.simple.codegen.RegAllocTestSupport.coldLoopSelfConflict(); }
+
     @Test public void testPrintingDeadFunction() throws Exception {
         var code = new CodeGen("return 0;").parse();
         var tfp = TypeFunPtr.TEST;
diff --git a/chapter25/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java b/chapter25/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java
index a92859d4..038d6882 100644
--- a/chapter25/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java
+++ b/chapter25/src/test/java/com/seaofnodes/simple/codegen/RegAllocTestSupport.java
@@ -209,6 +209,34 @@ public class RegAllocTestSupport {
         assertFalse("A fixed definition clobbers even before coloring",uncolored.sameBlockNoClobber(copy));
     }
 
+    public static void coldLoopSelfConflict() {
+        for( boolean phiConflict : new boolean[]{false,true} ) {
+            CodeGen code = graph();
+            RegAlloc alloc = new RegAlloc(code);
+            Op init = new Op(A,null,null,false,code._start);
+            LoopNode loop = new LoopNode(null,null,code._start);
+            PhiNode phi = new PhiNode("loop",loop,init,null);
+            phi._type = TypeInteger.BOT;
+            Op back = new Op(A,A,null,false,loop,phi);
+            phi.setDef(2,back);
+            Op use = new Op(null,A,null,false,loop,phi);
+            loop.setDef(2,loop);
+            LRG lrg = alloc.newLRG(phi,null);
+            lrg._mask = A;
+            alloc.union(lrg,init); alloc.union(lrg,back);
+            lrg.selfConflict(back);
+            if( phiConflict ) lrg.selfConflict(phi);
+            assertTrue(alloc.splitSelfConflict((byte)0,lrg));
+            assertSame(phi,use.in(1)); // First try leaves the hot definition alone.
+            assertSame(back,phi.in(2));
+            if( phiConflict ) assertTrue(phi.in(1) instanceof SplitNode);
+            // Even if the first attempt made no graph change, retry must split.
+            assertTrue(alloc.splitSelfConflict((byte)1,lrg));
+            assertTrue(phi.in(2) instanceof SplitNode);
+            if( phiConflict ) assertTrue(use.in(1) instanceof SplitNode);
+        }
+    }
+
     public static void coalescing() {
         // Merge, incompatible masks, interference, capacity, and adjacency remapping.
         for( int kind=0; kind<5; kind++ ) {
-- 
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