From ef7577136b942819d4cff2f8c63605744e854f75 Mon Sep 17 00:00:00 2001
From: Cliff Click <cliffc@acm.org>
Date: Sun, 11 May 2025 11:43:10 -0700
Subject: Clean up stacked mergemem

---
 .../com/seaofnodes/simple/node/MemMergeNode.java   | 32 ++++++++++++++++------
 .../java/com/seaofnodes/simple/node/StoreNode.java |  7 +++++
 2 files changed, 30 insertions(+), 9 deletions(-)

(limited to 'chapter22/src/main/java/com/seaofnodes')

diff --git a/chapter22/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java b/chapter22/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
index e936ee58..9f2fdd16 100644
--- a/chapter22/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
+++ b/chapter22/src/main/java/com/seaofnodes/simple/node/MemMergeNode.java
@@ -65,24 +65,38 @@ public class MemMergeNode extends Node {
     @Override public Node idealize() {
         if( inProgress() ) return null;
 
+        // Fold defaults into the default
+        boolean progress=false, allDefault=true;
+        for( int i=2; i<nIns(); i++ )
+            if( in(1) == in(i) ) { setDef(i,null); progress=true; }
+            else                 { allDefault=false; }
+
         // If not merging any memory (all memory is just the default)
-        if( allDefault() )
+        if( allDefault )
             return in(1);       // Become default memory
 
-        return null;
-    }
-    private boolean allDefault() {
-        for( int i=2; i<nIns(); i++ )
-            if( in(1) != in(i) )
-                return false;
-        return true;
+        // Collapse stacked all-mem
+        if( in(1) instanceof MemMergeNode mem ) {
+            // Goal is to swap my default mem with mem's default mem
+            for( int i=2; i<mem.nIns(); i++ ) {
+                if( mem.in(i) != null ) {
+                    // deeper default mem has a non-default
+                    if( i>=nIns() || in(i)==null )
+                        setDefX(i,mem.in(i));
+                }
+            }
+            setDef(1,mem.in(1));
+            return this;
+        }
+
+        return progress ? this : null;
     }
 
 
     public Node in( Var v ) { return in(v._idx); }
 
     public Node alias( int alias ) {
-        return in(alias<nIns() && in(alias)!=null ? alias : 1);
+        return alias < nIns() && in(alias)!=null ? in(alias) : in(1);
     }
 
     Node alias( int alias, Node st ) {
diff --git a/chapter22/src/main/java/com/seaofnodes/simple/node/StoreNode.java b/chapter22/src/main/java/com/seaofnodes/simple/node/StoreNode.java
index 2e9e38d5..9b561bed 100644
--- a/chapter22/src/main/java/com/seaofnodes/simple/node/StoreNode.java
+++ b/chapter22/src/main/java/com/seaofnodes/simple/node/StoreNode.java
@@ -71,6 +71,12 @@ public class StoreNode extends MemOpNode {
             return this;
         }
 
+        // Simple store-after-MemMerge to a known alias can bypass.  Happens when inlining.
+        if( mem() instanceof MemMergeNode mem ) {
+            setDef(1,mem.alias(_alias));
+            return this;
+        }
+
         // Value is automatically truncated by narrow store
         if( val() instanceof AndNode and && and.in(2)._type.isConstant()  ) {
             int log = _declaredType.log_size();
@@ -84,6 +90,7 @@ public class StoreNode extends MemOpNode {
             }
         }
 
+        // Store will chop high order bits off; math to change those bits can be dropped.
         if( val() instanceof SarNode shr &&
             shr.in(1) instanceof ShlNode shl &&
             shr.in(2)._type.isConstant() &&
-- 
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