8361144: Strenghten the Ideal Verification in PhaseIterGVN::verify_Ideal_for by comparing the hash of a node before and after Ideal

Co-authored-by: Emanuel Peter <epeter@openjdk.org>
Reviewed-by: galder, dfenacci, epeter

Author: 2 people

src/hotspot/share/opto/phaseX.cpp

@@ -1818,7 +1818,8 @@ bool PhaseIterGVN::verify_Ideal_for(Node* n, bool can_reshape) {
 
   // The number of nodes shoud not increase.
   uint old_unique = C->unique();
-
+  // The hash of a node should not change, this would indicate different inputs
+  uint old_hash = n->hash();
   Node* i = n->Ideal(this, can_reshape);
   // If there was no new Idealization, we are probably happy.
   if (i == nullptr) {
@@ -1832,6 +1833,16 @@ bool PhaseIterGVN::verify_Ideal_for(Node* n, bool can_reshape) {
       return true;
     }
 
+    if (old_hash != n->hash()) {
+      stringStream ss; // Print as a block without tty lock.
+      ss.cr();
+      ss.print_cr("Ideal optimization did not make progress but node hash changed.");
+      ss.print_cr("  old_hash = %d, hash = %d", old_hash, n->hash());
+      n->dump_bfs(1, nullptr, "", &ss);
+      tty->print_cr("%s", ss.as_string());
+      return true;
+    }
+
     verify_empty_worklist(n);
 
     // Everything is good.