From 81b654d76444d747fdf1d053760e507b50f26e18 Mon Sep 17 00:00:00 2001
From: Cliff Click <cliffc@acm.org>
Date: Mon, 5 Oct 2026 15:38:06 -0700
Subject: Small peep to drop simple store-updates out of loops

---
 .../src/test/java/com/seaofnodes/simple/Chapter11Test.java |  5 +++--
 .../src/test/java/com/seaofnodes/simple/Chapter19Test.java | 14 +++++++++++---
 .../src/test/java/com/seaofnodes/simple/Chapter20Test.java |  2 +-
 .../src/test/java/com/seaofnodes/simple/Chapter21Test.java |  4 ++--
 .../src/test/java/com/seaofnodes/simple/Chapter22Test.java |  4 ++--
 .../java/com/seaofnodes/simple/MemoryEncodingTest.java     |  6 +++---
 6 files changed, 22 insertions(+), 13 deletions(-)

(limited to 'chapter22/src/test/java')

diff --git a/chapter22/src/test/java/com/seaofnodes/simple/Chapter11Test.java b/chapter22/src/test/java/com/seaofnodes/simple/Chapter11Test.java
index a38e93c1..439333ca 100644
--- a/chapter22/src/test/java/com/seaofnodes/simple/Chapter11Test.java
+++ b/chapter22/src/test/java/com/seaofnodes/simple/Chapter11Test.java
@@ -36,7 +36,8 @@ public class Chapter11Test {
         var stop = code._stop;
         int[] phis = {0};
         stop.walk(n -> {
-            if (n instanceof MemPhiNode) phis[0]++;
+            // Store sinking can replace field memory Phis with value Phis.
+            if (n instanceof PhiNode) phis[0]++;
             if (n instanceof MemMergeNode m && m.in(1) instanceof BulkMemPhiNode b)
                 for(int a=b._aliases.nextSetBit(0); a>=0; a=b._aliases.nextSetBit(a+1))
                     assertTrue(a<m.nIns() && m.in(a)!=null);
@@ -44,7 +45,7 @@ public class Chapter11Test {
                 !(n instanceof MemPhiNode) && !(n instanceof BulkMemPhiNode) && !(n instanceof ParmNode));
             return null;
         });
-        assertTrue(phis[0]>=3);
+        assertTrue(phis[0]>=4); // Three fields and the loop counter.
         assertEquals("S{x=1,y=2,z=3}",Eval2.eval(code,4));
     }
 
diff --git a/chapter22/src/test/java/com/seaofnodes/simple/Chapter19Test.java b/chapter22/src/test/java/com/seaofnodes/simple/Chapter19Test.java
index e7b72e0a..dee7d928 100644
--- a/chapter22/src/test/java/com/seaofnodes/simple/Chapter19Test.java
+++ b/chapter22/src/test/java/com/seaofnodes/simple/Chapter19Test.java
@@ -385,13 +385,21 @@ return sq(arg) + sq(3);
 
     private static java.util.ArrayList<String> memoryPhis(Node stop) {
         var phis = new java.util.ArrayList<String>();
-        stop.walk(n -> {
+        // Count only definitions reachable from Stop, as instruction selection does.
+        // A dead Phi cycle can still appear through the reverse use edges.
+        var seen = new java.util.BitSet();
+        var work = new java.util.ArrayList<Node>();
+        work.add(stop);
+        for( int i=0; i<work.size(); i++ ) {
+            Node n = work.get(i);
+            if( n==null || seen.get(n._nid) ) continue;
+            seen.set(n._nid);
+            for( Node def : n._inputs ) work.add(def);
             if( n instanceof MemPhiNode phi ) phis.add("alias:"+phi._alias);
             if( n instanceof BulkMemPhiNode phi ) phis.add("bulk:"+phi._aliases);
             assertFalse(n instanceof PhiNode && n.isMem() &&
                 !(n instanceof MemPhiNode) && !(n instanceof BulkMemPhiNode) && !(n instanceof ParmNode));
-            return null;
-        });
+        }
         java.util.Collections.sort(phis);
         return phis;
     }
diff --git a/chapter22/src/test/java/com/seaofnodes/simple/Chapter20Test.java b/chapter22/src/test/java/com/seaofnodes/simple/Chapter20Test.java
index d5521c03..2ec29f99 100644
--- a/chapter22/src/test/java/com/seaofnodes/simple/Chapter20Test.java
+++ b/chapter22/src/test/java/com/seaofnodes/simple/Chapter20Test.java
@@ -242,7 +242,7 @@ hashCode(s);
         for( String cpu : new String[]{"x86_64_v2","riscv","arm"} )
             new CodeGen(src,com.seaofnodes.simple.type.TypeInteger.BOT,0)
                 .driver(CodeGen.Phase.Encoding,cpu,"SystemV");
-        testTarget(src,"x86_64_v2", "SystemV",9,null);
+        testTarget(src,"x86_64_v2", "SystemV",0,null);
         testTarget(src,"riscv"    , "SystemV",1,null);
         testTarget(src,"arm"      , "SystemV",0,null);
     }
diff --git a/chapter22/src/test/java/com/seaofnodes/simple/Chapter21Test.java b/chapter22/src/test/java/com/seaofnodes/simple/Chapter21Test.java
index 3d74f7a5..2c91de0d 100644
--- a/chapter22/src/test/java/com/seaofnodes/simple/Chapter21Test.java
+++ b/chapter22/src/test/java/com/seaofnodes/simple/Chapter21Test.java
@@ -310,8 +310,8 @@ public class Chapter21Test {
     @Test public void testInfinite() {
         String src = "struct S { int i; }; !S !s = new S; while(1) s.i++;";
         testCPU(src,"x86_64_v2", "SystemV",0,"return Top;");
-        testCPU(src,"riscv"    , "SystemV",2,"return Top;");
-        testCPU(src,"arm"      , "SystemV",2,"return Top;");
+        testCPU(src,"riscv"    , "SystemV",0,"return Top;");
+        testCPU(src,"arm"      , "SystemV",0,"return Top;");
     }
 
     @Test
diff --git a/chapter22/src/test/java/com/seaofnodes/simple/Chapter22Test.java b/chapter22/src/test/java/com/seaofnodes/simple/Chapter22Test.java
index 30152640..2d94b8f0 100644
--- a/chapter22/src/test/java/com/seaofnodes/simple/Chapter22Test.java
+++ b/chapter22/src/test/java/com/seaofnodes/simple/Chapter22Test.java
@@ -181,8 +181,8 @@ public class Chapter22Test {
     @Test public void testInfiniteReturn() {
         String src = "struct S { int i; }; !S !s = new S; while(1) s.i++; return s.i;";
         testCPU(src,"x86_64_v2","SystemV",0,"return Top;");
-        testCPU(src,"riscv","SystemV",2,"return Top;");
-        testCPU(src,"arm","SystemV",2,"return Top;");
+        testCPU(src,"riscv","SystemV",0,"return Top;");
+        testCPU(src,"arm","SystemV",0,"return Top;");
     }
 
 
diff --git a/chapter22/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java b/chapter22/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java
index 2776898f..4bd36256 100644
--- a/chapter22/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java
+++ b/chapter22/src/test/java/com/seaofnodes/simple/MemoryEncodingTest.java
@@ -142,12 +142,12 @@ public class MemoryEncodingTest {
     }
 
     @Test public void testNeverMemory() {
-        // A synthetic exit must retain both precise slices of a no-exit loop.
+        // A varying pointer prevents store sinking: the synthetic exit needs both slices.
         for( String target : new String[]{"x86_64_v2","riscv","arm"} ) {
             CodeGen code = new CodeGen("""
                 struct S { int x; int y; };
-                !S !a=new S;
-                if( arg ) while( 1 ) { a.x+=arg; a.y+=a.x; }
+                !S !a=new S; !S !b=new S; !S !p=a;
+                if( arg ) while( 1 ) { p.x+=arg; p.y+=p.x; p=p==a ? b : a; }
                 return a.x+a.y;
                 """).driver(CodeGen.Phase.LoopTree);
             assertNotNull(code._stop.walk(n -> {
-- 
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