From 9a5ca20d2537179f3a8e01762c8db6b52a4db2d9 Mon Sep 17 00:00:00 2001
From: Cliff Click <cliffc@acm.org>
Date: Sat, 3 Oct 2026 14:03:48 -0700
Subject: Chapter 17a: Mutability and Read-Only Views

---
 .../com/seaofnodes/simple/GlobalCodeMotion.java    | 53 +++-------------------
 1 file changed, 7 insertions(+), 46 deletions(-)

(limited to 'src/main/java/com/seaofnodes/simple/GlobalCodeMotion.java')

diff --git a/src/main/java/com/seaofnodes/simple/GlobalCodeMotion.java b/src/main/java/com/seaofnodes/simple/GlobalCodeMotion.java
index bb109fc9..eba99128 100644
--- a/src/main/java/com/seaofnodes/simple/GlobalCodeMotion.java
+++ b/src/main/java/com/seaofnodes/simple/GlobalCodeMotion.java
@@ -16,43 +16,6 @@ public abstract class GlobalCodeMotion {
         schedLate( stop);
     }
 
-    // ------------------------------------------------------------------------
-    // Backwards walk on the CFG only, looking for unreachable code - which has
-    // to be an infinite loop.  Insert a bogus never-taken exit to Stop, so the
-    // loop becomes reachable.  Also, set loop nesting depth
-    public static void fixLoops(StopNode stop) {
-        // Backwards walk from Stop, looking for unreachable code
-        BitSet visit = new BitSet();
-        HashSet<CFGNode> unreach = new HashSet<>();
-        unreach.add(Parser.START);
-        for( Node ret : stop._inputs )
-            ((ReturnNode)ret).walkUnreach(visit,unreach);
-        if( unreach.isEmpty() ) return;
-
-        // Forwards walk from unreachable, looking for loops with no exit test.
-        visit.clear();
-        for( CFGNode cfg : unreach )
-            walkInfinite(cfg,visit,stop);
-        // Set loop depth on remaining graph
-        unreach.clear();
-        visit.clear();
-        for( Node ret : stop._inputs )
-            ((ReturnNode)ret).walkUnreach(visit,unreach);
-        assert unreach.isEmpty();
-    }
-
-
-    // Forwards walk over previously unreachable, looking for loops with no
-    // exit test.
-    static private void walkInfinite( CFGNode n, BitSet visit, StopNode stop ) {
-        if( visit.get(n._nid) ) return; // Been there, done that
-        visit.set(n._nid);
-        if( n instanceof LoopNode loop )
-            loop.forceExit(stop);
-        for( Node use : n._outputs )
-            if( use instanceof CFGNode cfg )
-                walkInfinite(cfg,visit,stop);
-    }
 
     // ------------------------------------------------------------------------
     // Visit all nodes in CFG Reverse Post-Order, essentially defs before uses
@@ -66,18 +29,16 @@ public abstract class GlobalCodeMotion {
         // Reverse Post-Order on CFG
         for( int j=rpo.size()-1; j>=0; j-- ) {
             CFGNode cfg = rpo.get(j);
-            cfg.loopDepth();    // Pre-compute loop depth
+            cfg.loopDepth();
             for( Node n : cfg._inputs )
                 _schedEarly(n,visit);
             // In dead infinite loops, entire code blocks may be unreachable
             // from below.  Reach down from the CFG to their Phis so their
             // inputs are scheduled too.
-            if( cfg instanceof RegionNode ) {
-                int len = cfg.nOuts();
-                for( int i=0; i<len; i++ )
-                    if( cfg.out(i) instanceof PhiNode phi )
+            if( cfg instanceof RegionNode )
+                for( Node phi : cfg._outputs )
+                    if( phi instanceof PhiNode )
                         _schedEarly(phi,visit);
-            }
         }
     }
 
@@ -143,7 +104,7 @@ public abstract class GlobalCodeMotion {
 
                 // All uses done?
                 for( Node use : n._outputs )
-                    if( use!=null && late[use._nid]==null && !(use instanceof PhiNode) )
+                    if( use!=null && late[use._nid]==null )
                         continue outer; // Nope, await all uses done
 
                 // Loads need their memory inputs' uses also done
@@ -262,9 +223,9 @@ public abstract class GlobalCodeMotion {
     private static CFGNode anti_dep( LoadNode load, CFGNode stblk, CFGNode defblk, CFGNode lca, Node st, int[] anti ) {
         // Preserve the full store range for the earlier evaluator scheduler.
         // It places nodes independently of GCM and may hoist this store.
-        for( ; stblk != defblk; stblk = stblk.idom() ) {
+        for( ; stblk != defblk.idom(); stblk = stblk.idom() ) {
             // Store and Load overlap, need anti-dependence
-            if( !(stblk instanceof IfNode) && anti[stblk._nid]==load._nid ) {
+            if( anti[stblk._nid]==load._nid ) {
                 lca = stblk.domLCA(lca,null); // Raise Loads LCA
                 if( lca == stblk && st != null && st._inputs.find(load) == -1 ) // And if something moved,
                     st.addDef(load);   // Add anti-dep as well
-- 
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