From 349c23d0527569284a8bec67f27130c4358e056c Mon Sep 17 00:00:00 2001
From: fuhsnn <66062782+fuhsnn@users.noreply.github.com>
Date: Fri, 25 Sep 2026 07:25:49 +0800
Subject: Extend and backport SubNode peephole

---
 .../main/java/com/seaofnodes/simple/node/SubNode.java | 19 +++++++++++++++----
 1 file changed, 15 insertions(+), 4 deletions(-)

(limited to 'chapter12/src')

diff --git a/chapter12/src/main/java/com/seaofnodes/simple/node/SubNode.java b/chapter12/src/main/java/com/seaofnodes/simple/node/SubNode.java
index d8538277..d55cbb4e 100644
--- a/chapter12/src/main/java/com/seaofnodes/simple/node/SubNode.java
+++ b/chapter12/src/main/java/com/seaofnodes/simple/node/SubNode.java
@@ -39,13 +39,24 @@ public class SubNode extends Node {
 
     @Override
     public Node idealize() {
+        Node lhs = in(1);
+        Node rhs = in(2);
+        Type t1 = lhs._type;
+        Type t2 = rhs._type;
+
+        if( t2.isConstant() && t2 instanceof TypeInteger i && i.value()==0 )
+            return lhs;
+
+        if( t1.isConstant() && t1 instanceof TypeInteger i && i.value()==0 )
+            return new MinusNode(rhs);
+
         // x - (-y) is x+y
-        if( in(2) instanceof MinusNode minus )
-            return new AddNode(in(1),minus.in(1));
+        if( rhs instanceof MinusNode minus )
+            return new AddNode(lhs,minus.in(1));
 
         // (-x) - y is -(x+y)
-        if( in(1) instanceof MinusNode minus )
-            return new MinusNode(new AddNode(minus.in(1),in(2)).peephole());
+        if( lhs instanceof MinusNode minus )
+            return new MinusNode(new AddNode(minus.in(1),rhs).peephole());
 
         return null;
     }
-- 
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