8308749: C2 failed: regular loops only (counted loop inside infinite loop)

Reviewed-by: kvn, chagedorn

src/hotspot/share/opto/loopnode.cpp

@@ -1745,6 +1745,21 @@ bool PhaseIdealLoop::is_counted_loop(Node* x, IdealLoopTree*&loop, BasicType iv_
   // =================================================
   // ---- SUCCESS!   Found A Trip-Counted Loop!  -----
   //
+
+  if (x->Opcode() == Op_Region) {
+    // x has not yet been transformed to Loop or LongCountedLoop.
+    // This should only happen if we are inside an infinite loop.
+    // It happens like this:
+    //   build_loop_tree -> do not attach infinite loop and nested loops
+    //   beautify_loops  -> does not transform the infinite and nested loops to LoopNode, because not attached yet
+    //   build_loop_tree -> find and attach infinite and nested loops
+    //   counted_loop    -> nested Regions are not yet transformed to LoopNodes, we land here
+    assert(x->as_Region()->is_in_infinite_subgraph(),
+           "x can only be a Region and not Loop if inside infinite loop");
+    // Come back later when Region is transformed to LoopNode
+    return false;
+  }
+
   assert(x->Opcode() == Op_Loop || x->Opcode() == Op_LongCountedLoop, "regular loops only");
   C->print_method(PHASE_BEFORE_CLOOPS, 3);
 

test/hotspot/jtreg/compiler/loopopts/TestCountedLoopInsideInfiniteLoop.jasm

@@ -0,0 +1,60 @@
+/*
+ * Copyright (c) 2023, 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.
+ */
+
+super public class TestCountedLoopInsideInfiniteLoop
+{
+    public Method "<init>":"()V"
+    stack 2 locals 1
+    {
+        aload_0;
+        invokespecial  Method java/lang/Object."<init>":"()V";
+        return;
+    }
+    static Method test:"(IIII)V"
+    stack 200 locals 4
+    {
+        iload      0; // arg0 == 0
+        ifeq LEND;
+
+    LOOP1: // counted loop to kick off beautify_loops
+        iload      1;
+        ifeq LOOP1;
+        iload      2;
+        ifle LOOP1;
+
+    LOOP2: // infinite loop (still Region)
+        goto LOOP2b;
+
+    LOOP2b: // counted loop (still Region)
+        iinc       3, -1;
+        iload      3;
+        ifgt LOOP2b;
+
+        iconst_0;
+        ifeq LOOP2; // always true
+        goto LOOP2b;
+
+    LEND:
+        return;
+    }
+}

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

@@ -0,0 +1,39 @@
+/*
+ * Copyright (c) 2023, 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 8308749
+ * @compile TestCountedLoopInsideInfiniteLoop.jasm
+ * @summary Counted Loops inside infinite loops are only detected later,
+ *          and may still be a Region and not a LoopNode as expected.
+ * @run main/othervm -Xcomp -XX:-TieredCompilation -XX:PerMethodTrapLimit=0
+ *      -XX:CompileCommand=compileonly,TestCountedLoopInsideInfiniteLoop::test
+ *      TestCountedLoopInsideInfiniteLoopMain
+ */
+
+public class TestCountedLoopInsideInfiniteLoopMain {
+    public static void main (String[] args) {
+        TestCountedLoopInsideInfiniteLoop.test(0, 0, 0, 0);
+    }
+}