From c6afd3ced68d231a1d466bd62403409db9e8a96e Mon Sep 17 00:00:00 2001
From: Kerem Kat <krk@openjdk.org>
Date: Thu, 12 Mar 2026 09:24:55 +0000
Subject: [PATCH] 8379460: C2: Notify AddI/AddL to URShiftI/URShiftL users

Reviewed-by: qamai, dfenacci, mchevalier
---
 src/hotspot/share/opto/phaseX.cpp             |  7 ++
 .../c2/igvn/TestURShiftAddNotification.java   | 89 +++++++++++++++++++
 2 files changed, 96 insertions(+)
 create mode 100644 test/hotspot/jtreg/compiler/c2/igvn/TestURShiftAddNotification.java

diff --git a/src/hotspot/share/opto/phaseX.cpp b/src/hotspot/share/opto/phaseX.cpp
index c77316e7d0b..082746f80b7 100644
--- a/src/hotspot/share/opto/phaseX.cpp
+++ b/src/hotspot/share/opto/phaseX.cpp
@@ -2581,6 +2581,13 @@ void PhaseIterGVN::add_users_of_use_to_worklist(Node* n, Node* use, Unique_Node_
       return u->Opcode() == Op_CmpU;
     });
   }
+  // If changed AddI/AddL inputs, check URShift users for
+  // "((X << z) + Y) >>> z" optimization in URShift{I,L}Node::Ideal.
+  if (use_op == Op_AddI || use_op == Op_AddL) {
+    add_users_to_worklist_if(worklist, use, [](Node* u) {
+      return u->Opcode() == Op_URShiftI || u->Opcode() == Op_URShiftL;
+    });
+  }
   // If changed AndI/AndL inputs, check RShift/URShift users for "(x & mask) >> shift" optimization opportunity
   if (use_op == Op_AndI || use_op == Op_AndL) {
     add_users_to_worklist_if(worklist, use, [](Node* u) {
diff --git a/test/hotspot/jtreg/compiler/c2/igvn/TestURShiftAddNotification.java b/test/hotspot/jtreg/compiler/c2/igvn/TestURShiftAddNotification.java
new file mode 100644
index 00000000000..8ca192ea38b
--- /dev/null
+++ b/test/hotspot/jtreg/compiler/c2/igvn/TestURShiftAddNotification.java
@@ -0,0 +1,89 @@
+/*
+ * Copyright Amazon.com Inc. 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.
+ */
+package compiler.c2.igvn;
+
+import compiler.lib.ir_framework.*;
+import jdk.test.lib.Asserts;
+import jdk.test.lib.Platform;
+import jdk.test.lib.Utils;
+import java.util.Random;
+
+/*
+ * @test
+ * @bug 8379460
+ * @key randomness
+ * @summary When AddI/AddL inputs change during IGVN, URShift users must be re-added
+ *          to the IGVN worklist so they can re-check the ((X << z) + Y) >>> z optimization.
+ * @library /test/lib /
+ * @run driver ${test.main.class}
+ */
+public class TestURShiftAddNotification {
+
+    private static final Random RANDOM = Utils.getRandomInstance();
+
+    public static void main(String[] args) {
+        var framework = new TestFramework();
+        framework.addScenarios(new Scenario(0));
+        if (Platform.isDebugBuild()) {
+            framework.addScenarios(new Scenario(1, "-XX:VerifyIterativeGVN=1110"));
+        }
+        framework.start();
+    }
+
+    // The trick: a loop whose exit value is only known after loop optimization.
+    // During initial GVN, i is a Phi, so (x << C) * i stays as MulI — URShift
+    // can't see the LShiftI input through the MulI. After loop opts resolve
+    // i = 1, MulI identity-folds to LShiftI (same type, no cascade), and
+    // without the fix URShift is never re-notified about the new LShiftI input.
+
+    @Run(test = {"testI", "testL"})
+    public void runTests() {
+        int xi = RANDOM.nextInt();
+        int yi = RANDOM.nextInt();
+        long xl = RANDOM.nextLong();
+        long yl = RANDOM.nextLong();
+
+        Asserts.assertEQ(((xi << 3) + yi) >>> 3, testI(xi, yi));
+        Asserts.assertEQ(((xl << 9) + yl) >>> 9, testL(xl, yl));
+    }
+
+    @Test
+    @IR(failOn = {IRNode.LSHIFT_I, IRNode.MUL_I},
+        counts = {IRNode.URSHIFT_I, "1", IRNode.AND_I, "1"})
+    static int testI(int x, int y) {
+        int i;
+        for (i = -10; i < 1; i++) { }
+        int c = (x << 3) * i;
+        return (c + y) >>> 3;
+    }
+
+    @Test
+    @IR(failOn = {IRNode.LSHIFT_L, IRNode.MUL_L},
+        counts = {IRNode.URSHIFT_L, "1", IRNode.AND_L, "1"})
+    static long testL(long x, long y) {
+        int i;
+        for (i = -10; i < 1; i++) { }
+        long c = (x << 9) * i;
+        return (c + y) >>> 9;
+    }
+}