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

---
 .../java/com/seaofnodes/simple/Chapter11Test.java  |  5 ++-
 .../java/com/seaofnodes/simple/Chapter17bTest.java | 48 ++++++++++++++++++++++
 2 files changed, 51 insertions(+), 2 deletions(-)

(limited to 'chapter17b/src/test/java/com/seaofnodes')

diff --git a/chapter17b/src/test/java/com/seaofnodes/simple/Chapter11Test.java b/chapter17b/src/test/java/com/seaofnodes/simple/Chapter11Test.java
index 60ff05d8..f0caed02 100644
--- a/chapter17b/src/test/java/com/seaofnodes/simple/Chapter11Test.java
+++ b/chapter17b/src/test/java/com/seaofnodes/simple/Chapter11Test.java
@@ -34,7 +34,8 @@ public class Chapter11Test {
             """).parse().iterate();
         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);
@@ -42,7 +43,7 @@ public class Chapter11Test {
                 !(n instanceof MemPhiNode) && !(n instanceof BulkMemPhiNode));
             return null;
         });
-        assertTrue(phis[0]>=3);
+        assertTrue(phis[0]>=4); // Three fields and the loop counter.
         assertArrayEquals(new Object[]{1L,2L,3L},((Evaluator.Obj)Evaluator.evaluate(stop,4)).fields());
     }
 
diff --git a/chapter17b/src/test/java/com/seaofnodes/simple/Chapter17bTest.java b/chapter17b/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
index 976691fc..08c210fb 100644
--- a/chapter17b/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
+++ b/chapter17b/src/test/java/com/seaofnodes/simple/Chapter17bTest.java
@@ -2,6 +2,7 @@ package com.seaofnodes.simple;
 
 import com.seaofnodes.simple.evaluator.Evaluator;
 import com.seaofnodes.simple.node.StopNode;
+import com.seaofnodes.simple.node.StoreNode;
 import org.junit.Test;
 import org.junit.Ignore;
 import static org.junit.Assert.assertEquals;
@@ -9,6 +10,53 @@ import static org.junit.Assert.fail;
 
 public class Chapter17bTest {
 
+    @Test public void testSinkLoopStores() {
+        StopNode stop = new Parser("""
+            struct Totals { int sum; int visits; };
+            val t = new Totals { sum=7; visits=2; };
+            val data = new int[4];
+            for( int i=0; i<data#; i++ ) data[i]=arg+i;
+            for( int i=0; i<(arg<data# ? arg : data#); i++ ) {
+                t.sum = t.sum + data[i];
+                t.visits++;
+            }
+            return t;
+            """).parse().iterate();
+        stop.typeCheck();
+        int[] stores = {0};
+        stop.walk(n -> {
+            if( n instanceof StoreNode st && !st._name.equals("[]") ) {
+                assertEquals(stop.in(0).in(0),st.in(0)); // Both stores at the exit.
+                stores[0]++;
+            }
+            return null;
+        });
+        assertEquals(2,stores[0]);
+        for( int arg : new int[]{-1,0,1,3,4,5} ) {
+            long n = Math.max(0,Math.min(arg,4));
+            var obj = (Evaluator.Obj)Evaluator.evaluate(stop,arg);
+            org.junit.Assert.assertArrayEquals(new Object[]{7+n*arg+n*(n-1)/2,2+n},obj.fields());
+        }
+    }
+
+    @Test public void testKeepObservedLoopStore() {
+        StopNode stop = new Parser("""
+            struct S { int x; };
+            val a = new S;
+            val b = new S;
+            val p = arg ? a : b;
+            int sum=0;
+            for( int i=0; i<4; i++ ) {
+                a.x=i+1;
+                sum+=p.x;
+            }
+            return sum;
+            """).parse().iterate();
+        stop.typeCheck();
+        assertEquals(0L,Evaluator.evaluate(stop,0));
+        assertEquals(10L,Evaluator.evaluate(stop,1));
+    }
+
     @Test
     public void testJig() {
         Parser parser = new Parser("return 1;");
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