8333252: C2: assert(assertion_predicate_has_loop_opaque_node(iff)) failed: must find OpaqueLoop* nodes

Reviewed-by: kvn, epeter

src/hotspot/share/opto/loopPredicate.cpp

@@ -1212,7 +1212,13 @@ bool PhaseIdealLoop::loop_predication_impl_helper(IdealLoopTree* loop, IfProjNod
     // Limit is not exact.
     // Calculate exact limit here.
     // Note, counted loop's test is '<' or '>'.
+#ifdef ASSERT
+    const bool exact_trip_count = cl->has_exact_trip_count();
+    const uint trip_count = cl->trip_count();
     loop->compute_trip_count(this);
+    assert(exact_trip_count == cl->has_exact_trip_count() && trip_count == cl->trip_count(),
+           "should have computed trip count on Loop Predication entry");
+#endif
     Node* limit   = exact_limit(loop);
     int  stride   = cl->stride()->get_int();
 
@@ -1321,7 +1327,9 @@ IfProjNode* PhaseIdealLoop::add_template_assertion_predicate(IfNode* iff, IdealL
   max_value = new AddINode(opaque_init, max_value);
   register_new_node(max_value, new_proj);
   // init + (current stride - initial stride) is within the loop so narrow its type by leveraging the type of the iv Phi
-  max_value = new CastIINode(max_value, loop->_head->as_CountedLoop()->phi()->bottom_type());
+  const Type* type_iv = loop->_head->as_CountedLoop()->phi()->bottom_type();
+  assert(!type_iv->is_int()->is_con(), "constant indicates one loop iteration for which we bailed out earlier");
+  max_value = new CastIINode(max_value, type_iv);
   register_new_node(max_value, parse_predicate_proj);
 
   bol = rc_predicate(new_proj, scale, offset, max_value, limit, stride, rng, (stride > 0) != (scale > 0),
@@ -1350,12 +1358,21 @@ bool PhaseIdealLoop::loop_predication_impl(IdealLoopTree* loop) {
   CountedLoopNode *cl = nullptr;
   if (head->is_valid_counted_loop(T_INT)) {
     cl = head->as_CountedLoop();
-    // do nothing for iteration-splitted loops
-    if (!cl->is_normal_loop()) return false;
+    if (!cl->is_normal_loop()) {
+      // Do nothing for iteration-splitted loops
+      return false;
+    }
+    loop->compute_trip_count(this);
+    if (cl->trip_count() == 1) {
+      // Not worth to hoist checks out of a loop that is only run for one iteration since the checks are only going to
+      // be executed once anyway.
+      return false;
+    }
     // Avoid RCE if Counted loop's test is '!='.
     BoolTest::mask bt = cl->loopexit()->test_trip();
-    if (bt != BoolTest::lt && bt != BoolTest::gt)
+    if (bt != BoolTest::lt && bt != BoolTest::gt) {
       cl = nullptr;
+    }
   }
 
   Node* entry = head->skip_strip_mined()->in(LoopNode::EntryControl);

test/hotspot/jtreg/compiler/predicates/assertion/TestTemplateWithoutOpaqueLoopNodes.java

@@ -0,0 +1,69 @@
+/*
+ * Copyright (c) 2024, 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 id=Xcomp
+ * @bug 8333252
+ * @summary Test that no Template Assertion Predicate is created in Loop Prediction for one iteration loop.
+ * @run main/othervm -Xcomp -XX:CompileCommand=compileonly,*TestTemplateWithoutOpaqueLoopNodes::test
+ *                   compiler.predicates.assertion.TestTemplateWithoutOpaqueLoopNodes
+ */
+
+/*
+ * @test id=Xbatch
+ * @bug 8333252
+ * @summary Test that no Template Assertion Predicate is created in Loop Prediction for one iteration loop.
+ * @run main/othervm -Xbatch -XX:CompileCommand=compileonly,*TestTemplateWithoutOpaqueLoopNodes::test
+ *                   compiler.predicates.assertion.TestTemplateWithoutOpaqueLoopNodes
+ */
+
+package compiler.predicates.assertion;
+
+public class TestTemplateWithoutOpaqueLoopNodes {
+    static long lFld;
+    static long lArr[] = new long[10];
+
+    public static void main(String[] args) {
+        for (int i = 0; i < 10; i++) {
+            test();
+        }
+    }
+
+    static void test() {
+        int i16 = 1, i17, i19, i20 = 1, i22;
+        for (i17 = 6; i17 < 7; i17++) {
+            switch ((i16 >> 1) + 38) {
+                case 38:
+                    for (i19 = 1; i19 < 200000; i19++) {
+                    }
+                case 1:
+                    for (i22 = 1; i22 < 2; i22 += 2) {
+                        lArr[i22] = i20;
+                    }
+                    break;
+                case 4:
+                    lFld = 42;
+            }
+        }
+    }
+}