8264958: C2 compilation fails with assert "n is later than its clone"

Reviewed-by: neliasso, thartmann

Author: rwestrel

src/hotspot/share/opto/loopopts.cpp

@@ -1479,7 +1479,7 @@ void PhaseIdealLoop::split_if_with_blocks_post(Node *n) {
               IdealLoopTree* x_loop = get_loop(x_ctrl);
               Node* x_head = x_loop->_head;
               if (x_head->is_Loop() && (x_head->is_OuterStripMinedLoop() || x_head->as_Loop()->is_strip_mined())) {
-                if (is_dominator(n_ctrl, x_head)) {
+                if (is_dominator(n_ctrl, x_head) && n_ctrl != x_head) {
                   // Anti dependence analysis is sometimes too
                   // conservative: a store in the outer strip mined loop
                   // can prevent a load from floating out of the outer

test/hotspot/jtreg/compiler/loopstripmining/OuterStripMinedLoopLoadWronglyHoisted.java

@@ -0,0 +1,57 @@
+/*
+ * Copyright (c) 2021, Red Hat, Inc. 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 8264958
+ * @summary C2 compilation fails with assert "n is later than its clone"
+ *
+ * @run main/othervm -Xbatch OuterStripMinedLoopLoadWronglyHoisted
+ *
+ */
+
+
+public class OuterStripMinedLoopLoadWronglyHoisted {
+    int a;
+    int b;
+    short c;
+
+    void test() {
+        for (int i = 0; i < 10; ++i) {
+            a = c;
+            if (i > 1) {
+                b = 0;
+            }
+            c = (short)(b - 7);
+        }
+        a--;
+    }
+
+    public static void main(String[] args) {
+        OuterStripMinedLoopLoadWronglyHoisted t = new OuterStripMinedLoopLoadWronglyHoisted();
+        for (int i = 0; i < 100_000; ++i) {
+            t.test();
+        }
+    }
+}
+