8318049: C2: assert(!failure) failed: Missed optimization opportunity in PhaseIterGVN

Reviewed-by: epeter, thartmann

Author: jaskarth

src/hotspot/share/opto/phaseX.cpp

@@ -1594,17 +1594,18 @@ void PhaseIterGVN::add_users_to_worklist( Node *n ) {
       }
     }
 
-    // If changed Cast input, notify down for Phi and Sub - both do "uncast"
+    // If changed Cast input, notify down for Phi, Sub, and Xor - all do "uncast"
     // Patterns:
     // ConstraintCast+ -> Sub
     // ConstraintCast+ -> Phi
+    // ConstraintCast+ -> Xor
     if (use->is_ConstraintCast()) {
-      auto push_phi_or_sub_uses_to_worklist = [&](Node* n){
-        if (n->is_Phi() || n->is_Sub()) {
+      auto push_the_uses_to_worklist = [&](Node* n){
+        if (n->is_Phi() || n->is_Sub() || n->Opcode() == Op_XorI || n->Opcode() == Op_XorL) {
           _worklist.push(n);
         }
       };
-      ConstraintCastNode::visit_uncasted_uses(use, push_phi_or_sub_uses_to_worklist);
+      ConstraintCastNode::visit_uncasted_uses(use, push_the_uses_to_worklist);
     }
     // If changed LShift inputs, check RShift users for useless sign-ext
     if( use_op == Op_LShiftI ) {

test/hotspot/jtreg/compiler/c2/TestNotifyCastToXor.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2023, Oracle and/or its affiliates. All rights reserved.
+ * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
+ *
+ * This code is free software; you can redistribute it and/or modify it
+ * under the terms of the GNU General Public License version 2 only, as
+ * published by the Free Software Foundation.
+ *
+ * This code is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
+ * version 2 for more details (a copy is included in the LICENSE file that
+ * accompanied this code).
+ *
+ * You should have received a copy of the GNU General Public License version
+ * 2 along with this work; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
+ *
+ * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
+ * or visit www.oracle.com if you need additional information or have any
+ * questions.
+ */
+
+/*
+ * @test
+ * @bug 8318049
+ * @summary Test that xor nodes are properly notified when constraint casts change.
+ * @run main/othervm -Xcomp -XX:-TieredCompilation -XX:CompileOnly=compiler.c2.TestNotifyCastToXor::test
+                     -XX:+IgnoreUnrecognizedVMOptions -XX:VerifyIterativeGVN=10 compiler.c2.TestNotifyCastToXor
+ */
+
+package compiler.c2;
+
+public class TestNotifyCastToXor {
+    public static long longField = 0L;
+
+    public static void test() {
+        int ind = -15;
+
+        ind %= ind;
+        for (int i = 0; i < 40; ++i) {
+            int j = 1;
+
+            do {
+                ind ^= (int)longField;
+
+                // Dead loop
+                for (int k = 1; k < 1; k++) {
+                }
+            } while (j++ < 10);
+        }
+    }
+
+    public static void main(String[] args) {
+        test();
+    }
+}