8316361: C2: assert(!failure) failed: Missed optimization opportunity…

… in PhaseIterGVN with -XX:VerifyIterativeGVN=10

Backport-of: eeb63cd0fad9de1f7182ab97d0f25ac67745aa9e

src/hotspot/share/opto/loopTransform.cpp

@@ -2332,6 +2332,8 @@ void PhaseIdealLoop::do_unroll(IdealLoopTree *loop, Node_List &old_new, bool adj
     // can edit it's inputs directly.  Hammer in the new limit for the
     // minimum-trip guard.
     assert(opaq->outcnt() == 1, "");
+    // Notify limit -> opaq -> CmpI, it may constant fold.
+    _igvn.add_users_to_worklist(opaq->in(1));
     _igvn.replace_input_of(opaq, 1, new_limit);
   }
 

test/hotspot/jtreg/compiler/loopopts/TestNotifyOpaqueZeroTripGuardToCmpI.java

@@ -0,0 +1,48 @@
+/*
+ * 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 8316361
+ * @summary Test that if input to OpaqueZeroTripGuard changes, we notify down to CmpI.
+ * @run main/othervm -Xcomp -XX:+IgnoreUnrecognizedVMOptions -XX:VerifyIterativeGVN=10
+ *                   -XX:CompileCommand=compileonly,compiler.loopopts.TestNotifyOpaqueZeroTripGuardToCmpI::test
+ *                   compiler.loopopts.TestNotifyOpaqueZeroTripGuardToCmpI
+ */
+package compiler.loopopts;
+
+public class TestNotifyOpaqueZeroTripGuardToCmpI {
+    static int x, y;
+
+    public static void main(String[] strArr) {
+        test();
+    }
+
+    static void test() {
+        for (int i = 6; i < 43; i++) {
+            for (int j = i; j < 11; j++) {
+                x = y;
+            }
+        }
+    }
+}