8233529: loopTransform.cpp:2984: Error: assert(p_f->Opcode() == Op_IfFalse) failed

Strengthened asserts in locate_pre_from_main() and added a check for is_main_no_pre_loop().

Reviewed-by: kvn, vlivanov

src/hotspot/share/opto/loopTransform.cpp

@@ -2975,16 +2975,17 @@ void IdealLoopTree::adjust_loop_exit_prob(PhaseIdealLoop *phase) {
 }
 
 #ifdef ASSERT
-static CountedLoopNode* locate_pre_from_main(CountedLoopNode *cl) {
-  Node *ctrl  = cl->skip_predicates();
+static CountedLoopNode* locate_pre_from_main(CountedLoopNode* main_loop) {
+  assert(!main_loop->is_main_no_pre_loop(), "Does not have a pre loop");
+  Node* ctrl = main_loop->skip_predicates();
   assert(ctrl->Opcode() == Op_IfTrue || ctrl->Opcode() == Op_IfFalse, "");
-  Node *iffm = ctrl->in(0);
+  Node* iffm = ctrl->in(0);
   assert(iffm->Opcode() == Op_If, "");
-  Node *p_f = iffm->in(0);
+  Node* p_f = iffm->in(0);
   assert(p_f->Opcode() == Op_IfFalse, "");
-  CountedLoopEndNode *pre_end = p_f->in(0)->as_CountedLoopEnd();
-  assert(pre_end->loopnode()->is_pre_loop(), "");
-  return pre_end->loopnode();
+  CountedLoopNode* pre_loop = p_f->in(0)->as_CountedLoopEnd()->loopnode();
+  assert(pre_loop->is_pre_loop(), "No pre loop found");
+  return pre_loop;
 }
 #endif
 
@@ -3010,7 +3011,7 @@ void IdealLoopTree::remove_main_post_loops(CountedLoopNode *cl, PhaseIdealLoop *
   }
 
   CountedLoopNode* main_head = next_head->as_CountedLoop();
-  if (!main_head->is_main_loop()) {
+  if (!main_head->is_main_loop() || main_head->is_main_no_pre_loop()) {
     return;
   }
 

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

@@ -0,0 +1,75 @@
+/*
+ * 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 8233529
+ * @summary Verify that correct loops are selected when trying to remove main/post.
+ * @run main/othervm -XX:-TieredCompilation -Xbatch
+ *                   -XX:CompileCommand=compileonly,compiler.loopopts.TestRemoveMainPostLoops::test
+ *                   compiler.loopopts.TestRemoveMainPostLoops
+ */
+
+package compiler.loopopts;
+
+public class TestRemoveMainPostLoops {
+    static int cnt1 = 0;
+    int cnt2 = 0;
+
+    void testCallee() {
+        // (5) Only main and post loops are created (no pre loop -> "PeelMainPost") and main is unrolled.
+        for (int i = 0; i < 100; ++i) {
+            // (4) Inner loop is fully unrolled and removed.
+            for (int j = 0; j < 10; ++j) {
+                cnt1 += j;
+            }
+        }
+    }
+
+    void test() {
+        for (int i = 0; i < 10_000; ++i) {
+            // (0) testCallee method is inlined
+            testCallee();
+            cnt2 = 0;
+            // (1) OSR compilation is triggered in this loop.
+            // (2) Pre-/main-/post loops are created.
+            // (3) Main and post loops found empty and removed.
+            // (6) Pre loop is found empty, attempt to remove main and post loop then incorrectly selects main from (5).
+            for (int j = 0; j < 10; ++j) {
+                cnt2 = cnt1 + j;
+            }
+        }
+    }
+
+    public static void main(String[] strArr) {
+        TestRemoveMainPostLoops test = new TestRemoveMainPostLoops();
+        for (int i = 0; i < 100; i++) {
+            cnt1 = 0;
+            test.cnt2 = 0;
+            test.test();
+            if (cnt1 != 45000000 || test.cnt2 != 45000009) {
+                throw new RuntimeException("Incorrect result: " + cnt1 + " " + test.cnt2);
+            }
+        }
+    }
+}