Unify mixed-return checking and results

Unify dominator caching.

3 files changed, 31 insertions, 20 deletions

diff --git a/chapter10/src/main/java/com/seaofnodes/simple/node/LoopNode.java b/chapter10/src/main/java/com/seaofnodes/simple/node/LoopNode.java
index ea1489c4..a0ba973e 100644
--- a/chapter10/src/main/java/com/seaofnodes/simple/node/LoopNode.java
+++ b/chapter10/src/main/java/com/seaofnodes/simple/node/LoopNode.java
@@ -26,6 +26,6 @@ public class LoopNode extends RegionNode {
     }
 
     // Bypass Region idom, same as the default idom() using use entry in(1) instead of in(0)
-    @Override int idepth() { return _idepth(1); }
+    @Override int idepth() { return _idepth!=0 ? _idepth : cacheIDepth(entry().idepth()+1); }
     @Override Node idom() { return entry(); }
 }
diff --git a/chapter10/src/main/java/com/seaofnodes/simple/node/Node.java b/chapter10/src/main/java/com/seaofnodes/simple/node/Node.java
index c4889231..718b930d 100644
--- a/chapter10/src/main/java/com/seaofnodes/simple/node/Node.java
+++ b/chapter10/src/main/java/com/seaofnodes/simple/node/Node.java
@@ -565,9 +565,28 @@ public abstract class Node {
      * <p>
      * See {@link <a href="https://en.wikipedia.org/wiki/Dominator_(graph_theory)">...</a>}
      */
-    public int _idepth;         // IDOM depth approx; Zero is unset; non-zero is cached legit
-    final int _idepth(int idx) { return _idepth==0 ? (_idepth=in(idx).idepth()+1) : _idepth; }
-    int idepth() { return _idepth(0); }
+    public char _idepth;         // IDOM depth approx; Zero is unset; non-zero is cached legit
+
+    // Find the lowest common ancestor in the current dominator tree.
+    Node domLCA(Node rhs) {
+        if( rhs==null ) return this;
+        Node lhs = this;
+        while( lhs != rhs ) {
+            if( lhs==null || rhs==null ) return null;
+            int comp = lhs.idepth() - rhs.idepth();
+            if( comp >= 0 ) lhs = lhs.idom();
+            if( comp <= 0 ) rhs = rhs.idom();
+        }
+        return lhs;
+    }
+
+    int idepth() { return _idepth!=0 ? _idepth : cacheIDepth(idom().idepth()+1); }
+    // Zero depth means uncached. Check before narrowing so overflow cannot wrap.
+    final int cacheIDepth(int depth) {
+        assert 0 <= depth && depth <= Character.MAX_VALUE : "Dominator depth exceeds 65535";
+        return _idepth = (char)depth;
+    }
+
 
     // Return the immediate dominator of this Node.
     Node idom() { return in(0); }
diff --git a/chapter10/src/main/java/com/seaofnodes/simple/node/RegionNode.java b/chapter10/src/main/java/com/seaofnodes/simple/node/RegionNode.java
index 42501118..f7a56503 100644
--- a/chapter10/src/main/java/com/seaofnodes/simple/node/RegionNode.java
+++ b/chapter10/src/main/java/com/seaofnodes/simple/node/RegionNode.java
@@ -91,27 +91,19 @@ public class RegionNode extends Node {
     // Immediate dominator of Region is a little more complicated.
     @Override int idepth() {
         if( _idepth!=0 ) return _idepth;
-        int d=0;
+        int depth=0;
         for( Node n : _inputs )
             if( n!=null )
-                d = Math.max(d,n.idepth());
-        return _idepth=d;
+                depth = Math.max(depth,n.idepth()+1);
+        return cacheIDepth(depth);
     }
 
     @Override Node idom() {
-        if( nIns()==2 ) return in(1); // 1-input is that one input
-        if( nIns()!=3 ) return null;  // Fails for anything other than 2-inputs
-        // Walk the LHS & RHS idom trees in parallel until they match, or either fails.
-        // Because this does not cache, it can be linear in the size of the program.
-        Node lhs = in(1);
-        Node rhs = in(2);
-        while( lhs != rhs ) {
-          if( lhs==null || rhs==null ) return null;
-          var comp = lhs.idepth() - rhs.idepth();
-          if( comp >= 0 ) lhs = lhs.idom();
-          if( comp <= 0 ) rhs = rhs.idom();
-        }
-        return lhs;
+        Node lca = null;
+        // Recompute from predecessors: CFG edits can change the dominator.
+        for( int i=1; i<nIns(); i++ )
+            lca = in(i).domLCA(lca);
+        return lca;
     }
 
     // True if last input is null