8372302: C2: IGVN verification fails because ModXNode::Ideal creates unused intermediate nodes

Reviewed-by: epeter, qamai

src/hotspot/share/opto/divnode.cpp

@@ -1112,8 +1112,6 @@ Node *ModINode::Ideal(PhaseGVN *phase, bool can_reshape) {
   if( !ti->is_con() ) return nullptr;
   jint con = ti->get_con();
 
-  Node *hook = new Node(1);
-
   // First, special check for modulo 2^k-1
   if( con >= 0 && con < max_jint && is_power_of_2(con+1) ) {
     uint k = exact_log2(con+1);  // Extract k
@@ -1129,7 +1127,9 @@ Node *ModINode::Ideal(PhaseGVN *phase, bool can_reshape) {
       Node *x = in(1);            // Value being mod'd
       Node *divisor = in(2);      // Also is mask
 
-      hook->init_req(0, x);       // Add a use to x to prevent him from dying
+      // Add a use to x to prevent it from dying
+      Node* hook = new Node(1);
+      hook->init_req(0, x);
       // Generate code to reduce X rapidly to nearly 2^k-1.
       for( int i = 0; i < trip_count; i++ ) {
         Node *xl = phase->transform( new AndINode(x,divisor) );
@@ -1185,6 +1185,7 @@ Node *ModINode::Ideal(PhaseGVN *phase, bool can_reshape) {
   }
 
   // Save in(1) so that it cannot be changed or deleted
+  Node* hook = new Node(1);
   hook->init_req(0, in(1));
 
   // Divide using the transform from DivI to MulL
@@ -1407,8 +1408,6 @@ Node *ModLNode::Ideal(PhaseGVN *phase, bool can_reshape) {
   if( !tl->is_con() ) return nullptr;
   jlong con = tl->get_con();
 
-  Node *hook = new Node(1);
-
   // Expand mod
   if(con >= 0 && con < max_jlong && is_power_of_2(con + 1)) {
     uint k = log2i_exact(con + 1);  // Extract k
@@ -1426,13 +1425,15 @@ Node *ModLNode::Ideal(PhaseGVN *phase, bool can_reshape) {
       Node *x = in(1);            // Value being mod'd
       Node *divisor = in(2);      // Also is mask
 
-      hook->init_req(0, x);       // Add a use to x to prevent him from dying
+      // Add a use to x to prevent it from dying
+      Node* hook = new Node(1);
+      hook->init_req(0, x);
       // Generate code to reduce X rapidly to nearly 2^k-1.
       for( int i = 0; i < trip_count; i++ ) {
         Node *xl = phase->transform( new AndLNode(x,divisor) );
         Node *xh = phase->transform( new RShiftLNode(x,phase->intcon(k)) ); // Must be signed
         x = phase->transform( new AddLNode(xh,xl) );
-        hook->set_req(0, x);    // Add a use to x to prevent him from dying
+        hook->set_req(0, x);    // Add a use to x to prevent it from dying
       }
 
       // Generate sign-fixup code.  Was original value positive?
@@ -1482,6 +1483,8 @@ Node *ModLNode::Ideal(PhaseGVN *phase, bool can_reshape) {
   }
 
   // Save in(1) so that it cannot be changed or deleted
+  // Add a use to x to prevent him from dying
+  Node* hook = new Node(1);
   hook->init_req(0, in(1));
 
   // Divide using the transform from DivL to MulL

test/hotspot/jtreg/compiler/c2/igvn/TestModIdealCreatesUselessNode.java

@@ -0,0 +1,56 @@
+/*
+ * Copyright (c) 2025, 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.
+ */
+
+package compiler.c2.igvn;
+
+/*
+ * @test
+ * @bug 8372302
+ * @summary ModINode::Ideal and ModLNode::Ideal use an intermediate "hook" node
+ *          to keep stuff alive between phase->transform(...) calls. In some cases,
+ *          this node is not properly deleted before returning, causing failure
+ *          in the verification because the node count has changed. This test
+ *          ensures that the intermediate node gets destroyed before returning.
+ * @run main/othervm -XX:+IgnoreUnrecognizedVMOptions -XX:+UnlockDiagnosticVMOptions
+ *      -Xcomp -XX:-TieredCompilation
+ *      -XX:CompileCommand=compileonly,${test.main.class}::test*
+ *      -XX:VerifyIterativeGVN=1110
+ *      ${test.main.class}
+ * @run main ${test.main.class}
+ *
+ */
+
+public class TestModIdealCreatesUselessNode {
+    static int test0(int x) {
+        return x % Integer.MIN_VALUE;
+    }
+
+    static long test1(long x) {
+        return x % Long.MIN_VALUE;
+    }
+
+    public static void main(String[] args) {
+        test0(0);
+        test1(0L);
+    }
+}