From 2820c789fa6daf625b1f0f6bfe03a7c3eb428d09 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Manuel=20H=C3=A4ssig?= <mhaessig@openjdk.org>
Date: Mon, 1 Jun 2026 07:26:30 +0000
Subject: [PATCH] 8385408: C2: no reachable node should have no use

Reviewed-by: dlong, kvn
---
 src/hotspot/share/opto/mulnode.cpp            |  3 +-
 .../compiler/igvn/TestShiftWorklist.java      | 75 +++++++++++++++++++
 2 files changed, 77 insertions(+), 1 deletion(-)
 create mode 100644 test/hotspot/jtreg/compiler/igvn/TestShiftWorklist.java

diff --git a/src/hotspot/share/opto/mulnode.cpp b/src/hotspot/share/opto/mulnode.cpp
index 5e05d6a6e04..e48acd23b87 100644
--- a/src/hotspot/share/opto/mulnode.cpp
+++ b/src/hotspot/share/opto/mulnode.cpp
@@ -894,7 +894,8 @@ static Node* mask_and_replace_shift_amount(PhaseGVN* phase, Node* shift_node, ui
     }
 
     if (replace) {
-      shift_node->set_req(2, phase->intcon(masked_shift)); // Replace shift count with masked value.
+      // Replace shift count with masked value and put potential dead nodes on the worklist.
+      shift_node->set_req_X(2, phase->intcon(masked_shift), phase);
 
       // We need to notify the caller that the graph was reshaped, as Ideal needs
       // to return the root of the reshaped graph if any change was made.
diff --git a/test/hotspot/jtreg/compiler/igvn/TestShiftWorklist.java b/test/hotspot/jtreg/compiler/igvn/TestShiftWorklist.java
new file mode 100644
index 00000000000..64c5a5fe658
--- /dev/null
+++ b/test/hotspot/jtreg/compiler/igvn/TestShiftWorklist.java
@@ -0,0 +1,75 @@
+/*
+ * Copyright (c) 2026, 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 8385408
+ * @summary Test that inputs to removed shifts are put on the worklist and cleaned up
+ * @library /test/lib /
+ * @run main/othervm -Xbatch -XX:-TieredCompilation -XX:-UseOnStackReplacement
+ *                   -XX:CompileCommand=compileonly,${test.main.class}::test
+ *                   ${test.main.class}
+ * @run main ${test.main.class}
+ */
+
+package compiler.igvn;
+
+import jdk.test.lib.Asserts;
+
+public class TestShiftWorklist {
+    int N = 400;
+    int iArr[] = new int[N];
+
+    public static void main(String[] args) {
+        TestShiftWorklist t = new TestShiftWorklist();
+        for (int i = 0; i < 2_000; i++) {
+            int result = t.test();
+            Asserts.assertEQ(result, 0);
+        }
+    }
+
+    private int test() {
+        long[] lArr = new long[N];
+        long l = 1957; // l % 32 = 5
+        int n = 1;
+        for (int i = 1; i < 30; ++i) {
+            for (double j = 1; j < 12; j++) {
+                iArr[i] = 3;
+                for (long k = 1; k < 2; k++) {
+                    // C2 is able to prove that the effecive shift value for the int n is always 5.
+                    n >>= l;
+                }
+                l = 907436423360901L; // l % 32 = 5
+            }
+        }
+        return (int) checkSum(lArr);
+    }
+
+    private static long checkSum(long[] a) {
+        long sum = 0;
+        for (int j = 0; j < a.length; j++) {
+            sum += (a[j] / (j + 1) + a[j] % (j + 1));
+        }
+        return sum;
+    }
+}