8229994: assert(false) failed: Bad graph detected in get_early_ctrl_for_expensive

Fixes wrong idom information set in loop peeling when a loop strip mined loop is involved.

Reviewed-by: vlivanov, thartmann

src/hotspot/share/opto/loopTransform.cpp

@@ -654,8 +654,8 @@ void PhaseIdealLoop::do_peeling(IdealLoopTree *loop, Node_List &old_new) {
 
   // Step 4: Correct dom-depth info.  Set to loop-head depth.
 
-  int dd = dom_depth(head);
+  int dd = dom_depth(head->skip_strip_mined());
-  set_idom(head, head->in(1), dd);
+  set_idom(head->skip_strip_mined(), head->skip_strip_mined()->in(LoopNode::EntryControl), dd);
   for (uint j3 = 0; j3 < loop->_body.size(); j3++) {
     Node *old = loop->_body.at(j3);
     Node *nnn = old_new[old->_idx];

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

@@ -0,0 +1,84 @@
+/*
+ * Copyright (c) 2019, 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 8229994
+ * @summary Tests dominance in PhaseIdealLoop::get_early_ctrl_for_expensive() if an expensive SqrtD node is peeled.
+ *
+ * @run main/othervm -Xbatch -XX:-TieredCompilation
+ *                   -XX:CompileCommand=compileonly,compiler.loopopts.PeelingAndLoopStripMining::*
+ *                   compiler.loopopts.PeelingAndLoopStripMining
+ */
+
+package compiler.loopopts;
+
+public class PeelingAndLoopStripMining {
+
+    static double dFld = 3.3;
+
+    public void test(int k) {
+        for (int i = 1; i < 100; i++) {
+            // Loop invariant check triggers loop peeling
+            if (k == 300) {
+                return;
+            }
+
+            /*
+             * sqrtAdd() is inlined which contains an expensive node SqrtD with a control input from the above IfTrue node 'ifT'
+             * (flipped in IR, i.e. when not returning). PhaseIdealLoop::peeled_dom_test_elim() will change the control input
+             * of SqrtD to the peeled IfTrue node 'pifT' of 'ifT' and test if 'pifT' is on the idom chain starting from 'ifT'.
+             * This failed previously because the new loop entry from the peeled iteration was always set as idom of the
+             * CountedLoop node and not of the OuterStripMinedLoop node if present. Thus, 'pifT' was not found on the idom chain
+             * starting from 'ifT' resulting in a bad graph assertion failure in PhaseIdealLoop::get_early_ctrl_for_expensive().
+             */
+            dFld = sqrtAdd(i);
+        }
+    }
+
+    public static void main(String[] strArr) {
+        PeelingAndLoopStripMining _instance = new SubClass();
+        for (int i = 0; i < 10000; i++ ) {
+            _instance.test(12);
+        }
+
+        _instance = new PeelingAndLoopStripMining();
+        for (int i = 0; i < 10000; i++ ) {
+            _instance.test(300);
+        }
+        for (int i = 0; i < 10000; i++ ) {
+            _instance.test(45);
+        }
+    }
+
+    public double sqrtAdd(int i) {
+        return 1.0 + Math.sqrt(i);
+    }
+}
+
+class SubClass extends PeelingAndLoopStripMining {
+    public double sqrtAdd(int i) {
+        return 2.0 + Math.sqrt(i);
+    }
+}
+