8268360: Missing check for infinite loop during node placement

8268417: Add test from JDK-8268360

Reviewed-by: roland

Author: TheRealMDoerr

src/hotspot/share/opto/loopopts.cpp

@@ -1076,7 +1076,7 @@ static bool merge_point_safe(Node* region) {
 // For inner loop uses move it to the preheader area.
 Node *PhaseIdealLoop::place_near_use(Node *useblock) const {
   IdealLoopTree *u_loop = get_loop( useblock );
-  if (u_loop->_irreducible) {
+  if (u_loop->_irreducible || !u_loop->_head->is_Loop()) {
     return useblock;
   }
   if (u_loop->_child) {

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

@@ -0,0 +1,72 @@
+/*
+ * Copyright (c) 2021, 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 8268360
+ * @summary Test node placement when its use is inside infinite loop.
+ * @library /test/lib
+ * @run main/othervm -XX:CompileCommand=compileonly,compiler.loopopts.TestInfLoopNearUsePlacement::test
+ *                   compiler.loopopts.TestInfLoopNearUsePlacement
+ */
+
+package compiler.loopopts;
+
+import jdk.test.lib.Utils;
+
+public class TestInfLoopNearUsePlacement {
+
+    static void test() {
+        long loa[] = new long[42];
+
+        try {
+            for (int i = 0; i < 42; i++) {
+                Thread.sleep(1);
+                loa[i] = 42L;
+            }
+        } catch (InterruptedException e) {}
+
+        loa[0] = 1L;
+        // Infinite loop: loop's variable is reset on each iteration
+        for (int i = 0; i < 21; i++) {
+            loa[0] += 1L;
+            i = 1;
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        // Execute test in own thread because it contains an infinite loop
+        Thread thread = new Thread() {
+            public void run() {
+                for (int i = 0; i < 100; ++i) {
+                    test();
+                }
+            }
+        };
+        thread.setDaemon(true);
+        thread.start();
+        // Give thread some time to trigger compilation
+        Thread.sleep(Utils.adjustTimeout(5000));
+    }
+}