From 11aece21f4eb5b18af357b265bc27b80bcdbfbcb Mon Sep 17 00:00:00 2001
From: Emanuel Peter <epeter@openjdk.org>
Date: Fri, 9 Dec 2022 07:11:57 +0000
Subject: [PATCH] 8257197: Add additional verification code to PhaseCCP

Reviewed-by: chagedorn, kvn, thartmann
---
 src/hotspot/share/opto/phaseX.cpp | 48 +++++++++++++++++++++++++++++++
 src/hotspot/share/opto/phaseX.hpp |  4 +++
 2 files changed, 52 insertions(+)

diff --git a/src/hotspot/share/opto/phaseX.cpp b/src/hotspot/share/opto/phaseX.cpp
index d5c861e14aa..2c260ebf4f9 100644
--- a/src/hotspot/share/opto/phaseX.cpp
+++ b/src/hotspot/share/opto/phaseX.cpp
@@ -1782,6 +1782,7 @@ void PhaseCCP::analyze() {
   // Push root onto worklist
   Unique_Node_List worklist;
   worklist.push(C->root());
+  DEBUG_ONLY(Unique_Node_List worklist_verify;)
 
   assert(_root_and_safepoints.size() == 0, "must be empty (unused)");
   _root_and_safepoints.push(C->root());
@@ -1790,6 +1791,7 @@ void PhaseCCP::analyze() {
   // This loop is the meat of CCP.
   while (worklist.size() != 0) {
     Node* n = fetch_next_node(worklist);
+    DEBUG_ONLY(worklist_verify.push(n);)
     if (n->is_SafePoint()) {
       // Make sure safepoints are processed by PhaseCCP::transform even if they are
       // not reachable from the bottom. Otherwise, infinite loops would be removed.
@@ -1803,8 +1805,54 @@ void PhaseCCP::analyze() {
       push_child_nodes_to_worklist(worklist, n);
     }
   }
+  DEBUG_ONLY(verify_analyze(worklist_verify);)
 }
 
+#ifdef ASSERT
+// For every node n on verify list, check if type(n) == n->Value()
+// We have a list of exceptions, see comments in code.
+void PhaseCCP::verify_analyze(Unique_Node_List& worklist_verify) {
+  bool failure = false;
+  while (worklist_verify.size()) {
+    Node* n = worklist_verify.pop();
+    const Type* told = type(n);
+    const Type* tnew = n->Value(this);
+    if (told != tnew) {
+      // Check special cases that are ok
+      if (told->isa_integer(tnew->basic_type()) != nullptr) { // both either int or long
+        const TypeInteger* t0 = told->is_integer(tnew->basic_type());
+        const TypeInteger* t1 = tnew->is_integer(tnew->basic_type());
+        if (t0->lo_as_long() == t1->lo_as_long() &&
+            t0->hi_as_long() == t1->hi_as_long()) {
+          continue; // ignore integer widen
+        }
+      }
+      if (n->is_Load()) {
+        // MemNode::can_see_stored_value looks up through many memory nodes,
+        // which means we would need to notify modifications from far up in
+        // the inputs all the way down to the LoadNode. We don't do that.
+        continue;
+      }
+      tty->cr();
+      tty->print_cr("Missed optimization (PhaseCCP):");
+      n->dump_bfs(1, 0, "");
+      tty->print_cr("Current type:");
+      told->dump_on(tty);
+      tty->cr();
+      tty->print_cr("Optimized type:");
+      tnew->dump_on(tty);
+      tty->cr();
+      failure = true;
+    }
+  }
+  // If we get this assert, check why the reported nodes were not processed again in CCP.
+  // We should either make sure that these nodes are properly added back to the CCP worklist
+  // in PhaseCCP::push_child_nodes_to_worklist() to update their type or add an exception
+  // in the verification code above if that is not possible for some reason (like Load nodes).
+  assert(!failure, "Missed optimization opportunity in PhaseCCP");
+}
+#endif
+
 // Fetch next node from worklist to be examined in this iteration.
 Node* PhaseCCP::fetch_next_node(Unique_Node_List& worklist) {
   if (StressCCP) {
diff --git a/src/hotspot/share/opto/phaseX.hpp b/src/hotspot/share/opto/phaseX.hpp
index c51aed5b762..883dc92e7ef 100644
--- a/src/hotspot/share/opto/phaseX.hpp
+++ b/src/hotspot/share/opto/phaseX.hpp
@@ -603,6 +603,10 @@ class PhaseCCP : public PhaseIterGVN {
 
   // Worklist algorithm identifies constants
   void analyze();
+#ifdef ASSERT
+  // For every node n on verify list, check if type(n) == n->Value()
+  void verify_analyze(Unique_Node_List& worklist_verify);
+#endif
   // Recursive traversal of program.  Used analysis to modify program.
   virtual Node *transform( Node *n );
   // Do any transformation after analysis