2 files changed, 12 insertions, 3 deletions
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
@@ -113,6 +113,13 @@ public class Chapter04Test {
     }
 
     @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;");
         ReturnNode ret = parser.parse();