From c7a3752481c3c33cc7e460a75daf2a07d2c15c25 Mon Sep 17 00:00:00 2001
From: XmiliaH <45106915+XmiliaH@users.noreply.github.com>
Date: Sat, 28 Oct 2023 23:37:22 +0200
Subject: set_def might kill new_def in kill recursion caused by old_def being
 killed (#18)

---
 chapter04/src/main/java/com/seaofnodes/simple/node/Node.java     | 8 +++++---
 chapter04/src/test/java/com/seaofnodes/simple/Chapter04Test.java | 7 +++++++
 2 files changed, 12 insertions(+), 3 deletions(-)

(limited to 'chapter04')

diff --git a/chapter04/src/main/java/com/seaofnodes/simple/node/Node.java b/chapter04/src/main/java/com/seaofnodes/simple/node/Node.java
index 8d698d1b..7cc9291c 100644
--- a/chapter04/src/main/java/com/seaofnodes/simple/node/Node.java
+++ b/chapter04/src/main/java/com/seaofnodes/simple/node/Node.java
@@ -193,14 +193,16 @@ public abstract class Node {
     Node set_def(int idx, Node new_def ) {
         Node old_def = in(idx);
         if( old_def == new_def ) return this; // No change
+        // If new def is not null, add the corresponding def->use edge
+        // This needs to happen before removing the old node's def->use edge as
+        // the new_def might get killed if the old node kills it recursively.
+        if( new_def != null )
+            new_def._outputs.add(this);
         if( old_def != null &&  // If the old def exists, remove a def->use edge
             old_def.delUse(this) ) // If we removed the last use, the old def is now dead
             old_def.kill();     // Kill old def
         // Set the new_def over the old (killed) edge
         _inputs.set(idx,new_def);
-        // If new def is not null, add the corresponding def->use edge
-        if( new_def != null )
-            new_def._outputs.add(this);
         // Return self for easy flow-coding
         return this;
     }
diff --git a/chapter04/src/test/java/com/seaofnodes/simple/Chapter04Test.java b/chapter04/src/test/java/com/seaofnodes/simple/Chapter04Test.java
index 8cc78af0..4782e568 100644
--- a/chapter04/src/test/java/com/seaofnodes/simple/Chapter04Test.java
+++ b/chapter04/src/test/java/com/seaofnodes/simple/Chapter04Test.java
@@ -112,6 +112,13 @@ public class Chapter04Test {
         assertEquals("return (Proj_3+1);", ret.print());
     }
 
+    @Test
+    public void testChapter4Bug3() {
+        Parser parser = new Parser("int a=arg*2+1; a=a+-1; return a; #showGraph;", TypeInteger.BOT);
+        ReturnNode ret = parser.parse();
+        assertEquals("return (Proj_3*2);", ret.print());
+    }
+
     @Test
     public void testVarDecl() {
         Parser parser = new Parser("int a=1; return a;");
-- 
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